THOMPSON, Associate Judge:
In June 2012, appellant Craig Russell brought a lawsuit asserting “negligence— premises liability” and “strict liability/negligent failure to warn” claims against ap-pellee Call/D, LLC (“Call/D”), the owner of the apartment building where appellant was residing when he began to suffer the symptoms of Legionnaires’ disease, with which he was diagnosed in May 2011. Russell alleged in his Complaint and subsequent deposition that sewage back-ups in the apartment building and sewage-contaminated water that was allowed to stand in a vacant basement apartment, caused him to contract the disease. The Superior Court (the Honorable Natalia Combs Greene) granted Call/D’s motion
in limine
to exclude the testimony of Russell’s designated causation expert and then granted Call/D’s motion for summary judgment. Russell argues on appeal that Judge Combs Greene abused her discretion by ruling without considering his supplemental Super. Ct. Civ. R. 26(b)(4) statement and also that she erred in granting Call/ D’s motions
in limine
and for summary judgment. We disagree and therefore affirm.
I. Factual and Procedural Background
The following background facts, which we consider in the light most favorable to Russell,
are undisputed. In 2004, Russell leased an apartment on the second flooi; of 5218 Fitch Street, S.E. (Apartment 6), and lived there until May 2011. Sometime during the fall of 2010, the tenants living in the basement-level Apartment 1 vacated the premises, leaving behind their cats. The windows to Apartment 1 were left open, allowing the cats (and perhaps other animals) to enter and exit the vacant apartment. As a result, feces and dead animals were on the floor of the abandoned apartment, and the apartment had a horrible stench. The deposition testimony also establishes that in November 2010, a pipe burst in Apartment 1, causing flooding in the apartment. Additionally, sometime during or before May 2011, sewage and sewage-contaminated water backed up and overflowed into Apartment 1, covering its floor with a half-inch to inch of water that, at one point, also overflowed into the adjacent hallway. A video recording made on
May 28,. 2011 — after Russell had fallen ill with Legionnaires’ disease — shows that the apartment was still filthy at that time, with standing pools of water on the floor.
Around May 8, 2011, Russell noticed that the water coming out of the faucets in his apartment smelled bad and was discolored for several moments before running clean. Sewage or sewage-like water would also bubble up out of his drains after use. During early May 2011, the entire apartment building also began to smell, prompting residents to make calls to management starting around May 9, 2011.
On May 10, 2011, Russell began to feel fatigued. Over the next few days, he felt increasingly worse. On May 21, 2011, when he was barely able to stand, he went to the hospital and was diagnosed with Legionnaires’ disease, a serious form of pneumonia. Before the illness, Russell was a very healthy 89-year-old who routinely engaged in vigorous exercise.
The parties’ designated experts agree that
Legionella
bacteria, the cause of Legionnaires’ disease, infect humans through the inhalation of contaminated airborne water droplets; that is, the water source containing the bacteria must be aerosol-ized and inhaled. Legionnaires’ disease has an incubation period of 2-14 days, meaning that “symptoms typically manifest within 2 to 14 days after the exposure.”
During the two weeks before he became symptomatic, Russell went to many different places. He worked five days a week for ADT Security Systems as a service technician, a job that required him to go to an average of seven different locations every day. From May 6-8, 2011, Russell and his girlfriend were on a weekend trip to Bryce Resort, a ski resort in Mount Jackson, Virginia, where, according to the girlfriend’s deposition testimony, he took at least one shower.
No samples were taken of the stagnant-water in Apartment 1 before the apartment was professionally cleaned. Testing performed in September 2011 on water from taps and drain traps in Apartment 6 (to which Russell never returned after he was stricken in May 2011) uncovered no
Legionella
bacteria.. As far as the record reveals, no one else living in the Fitch Street apartment building and no one else who visited Bryce Resort during the same time period when Russell was there contracted Legionnaires’ disease.
As noted above, Russell filed his lawsuit in June 2012. On February 5, 2013, he served Call/D with a Rule 26(b)(4) statement in which he designated Dr. Steven Zimmet, a pulmonologist who treated Russell when he had Legionnaires’ disease, as an expert who would testify as to “how Legionnaires’ disease is contracted in general and specifically how Plaintiff contracted it due to his exposure to fumes and smells at his apartment building.”
No expert report or academic articles were attached to the Rule 26(b)(4) statement. Call/D’s attorneys deposed Dr. Zimmet on April 19, 2018. Although Russell’s counsel provided Dr. Zimmet. with two academic articles regarding
Legionella
bacteria immediately before the deposition, Dr. Zim-met testified that he did not rely on these articles in coming to the opinion about which he planned to testify at trial.
Dr. Zimmet assumed that Russell had regularly walked through sewage water when en
tering the apartment building, and he opined that Russell thereby came into contact with a sufficient number of aerosolized
Legionella
bacteria so as to become infected.
After the April 30, 2013, close of discovery, Call/D filed a motion
in limine
to exclude Dr. Zimmet’s testimony, arguing that his training and experience as a clinician in treating patients diagnosed with Legionnaires’ disease did not render him qualified to pinpoint the source of Russell’s exposure to
Legionella
bacteria. On October 15, 2013, Judge Combs Greene issued an Omnibus Order in which she granted Call/D’s motion
in limine
to exclude Dr. Zimmet’s testimony, reasoning in part that his testimony regarding the source of Russell’s illness was “entirely speculative.” That ruling was the premise for Judge Combs Greene’s additional ruling that there was “no genuine issue of material fact ... as to [the] proximate cause” of Russell’s illness and her granting of Call/ D’s motion for summary judgment.
II. Disregard of the Supplemental Rule 26(b)(4) Statement and the Decision Not to Hear Testimony from Dr. Zimmet
On September 18, 2013, Judge Combs Greene issued an order setting September 26, 2013, as the date for a hearing on Call/D’s motion
in limine.
She asked the parties to be prepared to address “[t]he basis for Dr. Zimm[e]t’s opinion that sewage is a possible source for
Legionella
bacteria,” the extent of Dr. Zimmet’s “knowledge concerning the sources of [the] infections” of- his previous patients who had been diagnosed with Legionnaires’ disease, and “[a]ny and all scholarly literature Dr.
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THOMPSON, Associate Judge:
In June 2012, appellant Craig Russell brought a lawsuit asserting “negligence— premises liability” and “strict liability/negligent failure to warn” claims against ap-pellee Call/D, LLC (“Call/D”), the owner of the apartment building where appellant was residing when he began to suffer the symptoms of Legionnaires’ disease, with which he was diagnosed in May 2011. Russell alleged in his Complaint and subsequent deposition that sewage back-ups in the apartment building and sewage-contaminated water that was allowed to stand in a vacant basement apartment, caused him to contract the disease. The Superior Court (the Honorable Natalia Combs Greene) granted Call/D’s motion
in limine
to exclude the testimony of Russell’s designated causation expert and then granted Call/D’s motion for summary judgment. Russell argues on appeal that Judge Combs Greene abused her discretion by ruling without considering his supplemental Super. Ct. Civ. R. 26(b)(4) statement and also that she erred in granting Call/ D’s motions
in limine
and for summary judgment. We disagree and therefore affirm.
I. Factual and Procedural Background
The following background facts, which we consider in the light most favorable to Russell,
are undisputed. In 2004, Russell leased an apartment on the second flooi; of 5218 Fitch Street, S.E. (Apartment 6), and lived there until May 2011. Sometime during the fall of 2010, the tenants living in the basement-level Apartment 1 vacated the premises, leaving behind their cats. The windows to Apartment 1 were left open, allowing the cats (and perhaps other animals) to enter and exit the vacant apartment. As a result, feces and dead animals were on the floor of the abandoned apartment, and the apartment had a horrible stench. The deposition testimony also establishes that in November 2010, a pipe burst in Apartment 1, causing flooding in the apartment. Additionally, sometime during or before May 2011, sewage and sewage-contaminated water backed up and overflowed into Apartment 1, covering its floor with a half-inch to inch of water that, at one point, also overflowed into the adjacent hallway. A video recording made on
May 28,. 2011 — after Russell had fallen ill with Legionnaires’ disease — shows that the apartment was still filthy at that time, with standing pools of water on the floor.
Around May 8, 2011, Russell noticed that the water coming out of the faucets in his apartment smelled bad and was discolored for several moments before running clean. Sewage or sewage-like water would also bubble up out of his drains after use. During early May 2011, the entire apartment building also began to smell, prompting residents to make calls to management starting around May 9, 2011.
On May 10, 2011, Russell began to feel fatigued. Over the next few days, he felt increasingly worse. On May 21, 2011, when he was barely able to stand, he went to the hospital and was diagnosed with Legionnaires’ disease, a serious form of pneumonia. Before the illness, Russell was a very healthy 89-year-old who routinely engaged in vigorous exercise.
The parties’ designated experts agree that
Legionella
bacteria, the cause of Legionnaires’ disease, infect humans through the inhalation of contaminated airborne water droplets; that is, the water source containing the bacteria must be aerosol-ized and inhaled. Legionnaires’ disease has an incubation period of 2-14 days, meaning that “symptoms typically manifest within 2 to 14 days after the exposure.”
During the two weeks before he became symptomatic, Russell went to many different places. He worked five days a week for ADT Security Systems as a service technician, a job that required him to go to an average of seven different locations every day. From May 6-8, 2011, Russell and his girlfriend were on a weekend trip to Bryce Resort, a ski resort in Mount Jackson, Virginia, where, according to the girlfriend’s deposition testimony, he took at least one shower.
No samples were taken of the stagnant-water in Apartment 1 before the apartment was professionally cleaned. Testing performed in September 2011 on water from taps and drain traps in Apartment 6 (to which Russell never returned after he was stricken in May 2011) uncovered no
Legionella
bacteria.. As far as the record reveals, no one else living in the Fitch Street apartment building and no one else who visited Bryce Resort during the same time period when Russell was there contracted Legionnaires’ disease.
As noted above, Russell filed his lawsuit in June 2012. On February 5, 2013, he served Call/D with a Rule 26(b)(4) statement in which he designated Dr. Steven Zimmet, a pulmonologist who treated Russell when he had Legionnaires’ disease, as an expert who would testify as to “how Legionnaires’ disease is contracted in general and specifically how Plaintiff contracted it due to his exposure to fumes and smells at his apartment building.”
No expert report or academic articles were attached to the Rule 26(b)(4) statement. Call/D’s attorneys deposed Dr. Zimmet on April 19, 2018. Although Russell’s counsel provided Dr. Zimmet. with two academic articles regarding
Legionella
bacteria immediately before the deposition, Dr. Zim-met testified that he did not rely on these articles in coming to the opinion about which he planned to testify at trial.
Dr. Zimmet assumed that Russell had regularly walked through sewage water when en
tering the apartment building, and he opined that Russell thereby came into contact with a sufficient number of aerosolized
Legionella
bacteria so as to become infected.
After the April 30, 2013, close of discovery, Call/D filed a motion
in limine
to exclude Dr. Zimmet’s testimony, arguing that his training and experience as a clinician in treating patients diagnosed with Legionnaires’ disease did not render him qualified to pinpoint the source of Russell’s exposure to
Legionella
bacteria. On October 15, 2013, Judge Combs Greene issued an Omnibus Order in which she granted Call/D’s motion
in limine
to exclude Dr. Zimmet’s testimony, reasoning in part that his testimony regarding the source of Russell’s illness was “entirely speculative.” That ruling was the premise for Judge Combs Greene’s additional ruling that there was “no genuine issue of material fact ... as to [the] proximate cause” of Russell’s illness and her granting of Call/ D’s motion for summary judgment.
II. Disregard of the Supplemental Rule 26(b)(4) Statement and the Decision Not to Hear Testimony from Dr. Zimmet
On September 18, 2013, Judge Combs Greene issued an order setting September 26, 2013, as the date for a hearing on Call/D’s motion
in limine.
She asked the parties to be prepared to address “[t]he basis for Dr. Zimm[e]t’s opinion that sewage is a possible source for
Legionella
bacteria,” the extent of Dr. Zimmet’s “knowledge concerning the sources of [the] infections” of- his previous patients who had been diagnosed with Legionnaires’ disease, and “[a]ny and all scholarly literature Dr. Zimm[e]t used to guide or assist him in reaching his conclusion that sewage can be a source of the
Legionella
bacteria.” Judge Combs Greene also stated that, while she found Dr. Zimmet’s attendance “essential,” his attendance would be excused if the scheduled hearing was inconvenient and if Russell could provide sufficient answers and documentation to address the court’s concerns. Alternatively, Judge Combs Greene would “consider Dr. Zimm[e]t’s appearance by telephone” if the parties agreed. Two days before the scheduled hearing, apparently while Judge Combs Greene was on leave, Russell’s counsel advised the judge’s staff that Dr. Zimmet would be unable to attend a hearing on September 26 and requested a continuance until September 27.
Staff instructed the parties to appear at the scheduled time. During the September 26 hearing, Russell’s counsel gave the court the two academic articles counsel had shown Dr. Zimmet prior to his deposition.
On September 30, 2013, four days after the hearing, Russell filed a supplemental Rule 26(b)(4) statement (“the supplemental statement”). The supplemental statement slightly amended the earlier description of Dr. Zimmet’s expected testimony, and attached to it were a number of journal articles and other publications. In her October 15, 2013, order granting Call/ D’s motion
in limine,
Judge Combs Greene stated that she “did not view or consider” the supplemental statement in ruling on the motion. Russell now contends that Judge Combs Greene abused her discretion in ruling on the motion
in limine
without reading the supplemental statement and without hearing testimony from Dr. Zimmet.
This court reviews a trial judge’s decision whether to accept a supplemental Rule 26(b)(4) statement for abuse of discretion.
See Ferrell v. Rosenbaum,
691 A.2d 641, 646 (D.C.1997). We “take into
account the reason for the supplement, the importance of the proffered testimony and any prejudice to the opposing party.”
Id.
at 647. In this case, we can find no abuse of discretion in Judge Combs Greene’s decision not to consider Russell’s supplemental statement. Russell was made aware by (1) the questioning at Dr. Zimmet’s deposition on April 19, 2013, (2) Call/D’s May 15, 2013, motion
in limine,
and (3) the affidavits of Call/D’s experts attached to Call/D’s May 15, 2013, motion for summary judgment (to which Russell filed an opposition on May 24, 2013), that Call/D was challenging Dr. Zimmet’s qualifications to testify, but Russell waited until September 30, 2013, to file the supplemental statement. Russell provided Judge Combs Greene (and he has provided this court) with no explanation for the delay; quite the contrary, his counsel asserted that Dr. Zimmet’s deposition was “very clear[,]” never mentioned a need to supplement the expert witness statement, and did not request leave to do so.
Nor do we discern that the information provided by the supplemental statement was important for appellant’s case. The supplemental statement slightly modified the description of Dr. Zimmet’s anticipated trial testimony: the earlier statement said that he would testify about how Russell contracted Legionnaires’ disease “due to his exposure to fumes and smells at his apartment building[,]” while the supplemental statement said that Dr. Zimmet would testify about how Russell contracted Legionnaires’ disease “due to his exposure to
stagnant water
and their [sic] associated fumes and smells at his apartment building” (emphasis added). The supplemental statement’s references to “stagnant water” and “longstanding stagnant water” were new, but Judge Combs Greene could see, from Dr. Zimmet’s deposition, that his opinion was that “sewage water was the most likely source of [Russell’s] exposure[,]” meaning that Russell cannot establish prejudice from the court’s not having read the revised text.
The publications attached to the supplemental statement and the citations to some of them in the text of the statement did add something new, because some of them pertain to investigations of the presence of
Legionella
bacteria in sewage treatment plants. However, nothing in the supplemental statement indicated that Dr. Zim-met had approved the statement or had ever read the articles and publications attached to it.
Dr. Zimmet testified at his
deposition that he arrived at his opinion about the source of Russell’s exposure without relying on journal articles,
and, as Judge Combs Greene recognized, Call/D could rightly claim prejudice from a late supplemental statement that “would potentially subject them to different allegations ... at a late stage of the litigation.”
French v. Levitt,
997 A.2d 701, 704 (D.C. 2010).
As for the court’s not hearing testimony from Dr. Zimmet before ruling on the
motion
in limine,
Russell highlights Judge Combs Greene’s statement (in the order setting the. hearing) that the description of Dr. Zimmet’s testimony in Russell’s Rule 26(b)(4) statement was “very vague.” But Judge Combs Greene told the parties at the outset of the hearing that she had probably been “overly cautious” in scheduling the hearing and thought she could rule on the motion after rereading Dr. Zimmet’s deposition, without hearing from him.
We discern no reason to question
Judge Combs Greene’s assessment, especially since we, too, think that Dr. Zim-met’s deposition furnished a sufficiently clear basis for the court to rule on the motion
in
limine.
Thus, we cannot agree with Russell’s claim that Judge Combs Greene abused her discretion by ruling “when she lacked the very information ... she needed to make an informed decision[.]”
III. The Ruling on Call/D’s Motion
In Limine
Russell contends that Judge Combs Greene also abused her discretion in excluding Dr. Zimmet’s testimony, arguing that Dr. Zimmet’s “training and experience provided a sufficient foundation to permit his expert opinion testimony on the issue of the source of [Russell’s] exposure to
Legionella
bacteria.” We review a trial court’s decision about whether to admit expert testimony for abuse of discretion.
District of Columbia v. Anderson,
597 A.2d 1295, 1299 (D.C.1991). That means that our review is deferential, as “deference ... is the hallmark of abuse of discretion review.”
General Elec. Co. v. Joiner,
522 U.S. 136, 143, 118 S.Ct. 512, 139 L.Ed.2d 508 (1997);
see also Girardot v. United States,
92 A.3d 1107, 1113 (D.C. 2014) (“The concept of ‘exercise of discretion’ is a review-restraining one.” (quoting
Johnson v. United States,
398 A.2d 354, 362 (D.C.1979))). Accordingly, the trial court’s decision will be “sustained unless it is manifestly erroneous.”
Coates v. United States,
558 A.2d 1148, 1152 (D.C.1989).
To be permitted to testify as an expert, a witness “must have sufficient skill, knowledge, or experience in that field or calling as to make it appear that his opinion or inference will probably aid the trier in his search for truth[.]”
Dyas v. United States,
376 A.2d 827, 832 (D.C. 1977) (citation omitted). “Implicit in that requirement is that the expert [must] have a reliable basis for [his] theory steeped in fact or adequate data, as opposed to offering a mere guess or conjecture.”
Perkins v. Hansen,
79 A.3d 342, 345 (D.C.2013) (citation and internal quotation marks omitted). “The purpose of expert opinion testimony is to avoid jury findings based on mere speculation or conjecture[,]” and thus the court must weigh the “sufficiency of the foundation for those opinions ... with this purpose in mind.”
Washington v. Washington Hosp. Ctr.,
579 A.2d 177, 181 (D.C.1990). “Without more than credentials and a subjective opinion, an expert’s testimony that ‘it is so’ is not admissible.”
Wilson Sporting Goods Co. v. Hickox,
59 A.3d 1267, 1273 (D.C.2013) (quoting
Viterbo v. Dow Chem. Co.,
826 F.2d 420, 424 (5th Cir.1987)). “Expert testimony may be excluded when the expert is unable to show a reliable basis for their theory.”
Haidak v. Corso,
841 A.2d 316, 327 (D.C.2004).
In this case, Judge Combs Greene articulated many reasons for her ruling that Dr. Zimmet was “not qualified to testify as to the source of [Russell’s] disease,” among them that Dr. Zimmet had never been trained in or “involved with the identification of the source of exposure” of Legion
naires’ disease, was “not aware of any specific type of bacteria present in sewage water[,]” “did not indicate any literature to support his belief that
Legionella
bacteria could exist in sewage water[,]” had “never had responsibility for determining the source of a person’s Legionella bacterial exposure as part of his clinical practiee[,]” did not know “what strains of Legionella bacteria are most commonly associated with Legionnaire’s [sic] Disease in humans[,]” was not familiar with the temperatures at which or the conditions under which
Legionella
bacteria amplify, and had “no data to support his opinion that Le-gionella bacteria [were] at sufficient levels [in Apartment 1] to cause [Russell’s] Legionnaire’s [sic] disease.” Dr. Zimmet’s deposition answers support these findings as well as Judge Combs Greene’s finding that his opinion testimony on causation was “without factual basis.”
It is true that, as Russell emphasizes, an expert witness may rely upon his experience alone when providing an opinion,
see Perkins,
79 A.3d at 345 (“[A] physician’s experience may provide a reliable basis for his or her expert opinion.”), and that an expert witness need not cite a peer-reviewed journal article as the basis for every opinion he provides and need not use the “data that will provide the highest degree of certainty[.]”
Id.
at 346. In addition, “[w]here an expert otherwise reliably utilizes scientific methods to reach a conclusion, lack of textual support may ‘go to the weight, not the admissibility’ of the expert’s testimony.”
Knight v. Kirby Inland Marine Inc.,
482 F.3d 347, 354 (5th Cir.2007). But, as Judge Combs Greene recognized, Dr. Zimmet relied on neither experience in investigating the source of a
Legionella
infection, nor knowledge about what had been determined to be the source of his other Legionnaires’ disease patients’ exposures, nor peer-reviewed journal articles, nor data from testing at the apartment building, and he did not utilize a scientific method to conclude that
Legionella
bacteria were present in the Fitch Street apartment building.
Instead, as he acknowledged during his deposition, he “essentially ma[de] the assumption ... that the water in the apartment [building] contained amplified levels of Legionella bacteria.” He acknowledged that the same logic by which he eliminated the environment at the Bryce Resort as a source of Russell’s infection — that “[n]obody else got sick” there — was equally applicable to the Fitch Street apartment building (since no one else living in the apartment building got sick), and he offered only the “beliefs]” that “taking a couple of showers” at Bryce would not be enough to make the previously healthy Russell sick and that Russell “really had no other source of Legionella disease.”
Further, Dr. Zimmet invoked “common sense” and “intuiti[on]” as his basis for saying that the Bryce Resort was not a probable source of Russell’s infection and that Russell’s “walking] through ... sew
er water” at the apartment building was the likely culprit.
And, when asked at his deposition about his “training, knowledge and experience with respect to being able to connect a diagnosis of Legionnaire’s [sic] disease to a suspected souree[,]” Dr. Zimmet answered that the basis of his opinion in this ease was that “[y]ou know it when you see it.” That response — I know it when I see it — was the “quintessential
ipse dixit
justification.”
TASER Int’l, Inc. v. Karbon Arms, LLC,
No. 11-426, 2013 WL 6773663, at *1 (D.Del. Dec. 19, 2013). Judge Combs Greene was not required to admit opinion evidence that was “connected to existing data only by the
ipse dixit
of the expert.”
Kumho Tire Co., Ltd. v. Carmichael,
526 U.S. 137, 157, 119 S.Ct. 1167, 143 L.Ed.2d 238 (1999) (quoting
Joiner,
522 U.S. at 146, 118 S.Ct. 512);
cf. Brown v. Bray & Gillespie III Mgmt. LLC,
No. 6:06-cv-661-Orl-22GJK, 2008 WL 2397601, at *6 (M.D.Fla. June 10, 2008) (concluding that an internist’s opinion that plaintiffs “contracted] an acute
Legionella
infection as a result of [their] hotel stay ... at the Sea Garden Inn in Florida” “lack[ed] a substantial basis,” and explaining that “[t]he opinions of an expert will not be accepted if based on merely the
ipse dixit
of the expert”).
Russell further contends that Judge Combs Greene “impermissibly demanded that [he] adduce direct (rather than circumstantial) evidence of the presence of
Legionella
bacteria in the building before permitting Dr. Zimmet to testify.” While we agree that the source of a plaintiffs Legionnaires’ infection can be proven by (and perhaps can be proven
only
by) circumstantial evidence,
we reject Russell’s claim of error, because we do not agree that Judge Combs Greene excluded Dr. Zimmet’s testimony on the ground that
he had no direct evidence of the presence of
Legionella
in the building. Judge Combs Greene found it “significante ]” that Dr. Zimmet “did not indicate any literature to support his belief that
Legionella
bacteria could exist in sewage water.” She reasoned that Dr. Zimmet’s opinion that sewage water was the most likely source of Russell’s exposure was “not supported by published scholarly data” and that Dr. Zimmet was “unfamiliar with several areas of scientific scholarship or clinical work
that might provide a substantive basis for the conclusion offered
” (emphasis added). She also cited portions of Dr. Zimmet’s deposition in which he testified that he did not regularly read “published medical or scientific or hygiene literature with respect to Legionnaire[s’] disease”; that he had formed his opinions in this case before seeing, just prior to his deposition, an article Russell’s counsel had given him entitled “Health Effects of Sewage Aerosols: Additional Serological Surveys and Search for
Legionella Pneumophila
in Sewage”; that the article would not play a role in the opinions he would render in the case; and that he had not reviewed any peer-reviewed and published literature discussing the prevalence of
Legionella
in sewage-contaminated water. In addition, Judge Combs Greene explicitly recognized that case law has held that “it is not an abuse of discretion for courts to allow expert testimony when the expert did not conduct independent testing” and that “[a]s long as the expert relied on published data generated by another expert in the pertinent field, the opinion is' admissible.” We read all these statements in the Omnibus Order as indicating that even though Dr. Zimmet had no direct evidence that
Legionella
bacteria were in water at the apartment building, Judge Combs Greene would likely have permitted him to testify if he had had a basis in the scientific literature to say that the sewage-contaminated water in the basement of the apartment building was a more likely source of Russell’s exposure than a shower at Bryce Resort or any of the scores of locations Russell had visited through his work and other activities during the incubation period.
We next address Russell’s contention that Judge Combs Greene applied a legally erroneous standard in ruling on the motion
in limine.
He argues that the judge held Dr. Zimmet “to a burden of proof greater than the preponderance of evidence (more likely than not) standard[.]”
The evidence of this error, he asserts, is the following statement on page 9 of Combs Greene’s Omnibus Order: “Dr. Zimmet concludes that he ‘believes’ that the sewage water was the most likely source of exposure as compared to the other possible sources because it looked like a ‘cesspool’ ” (bold font in the original). We note that Judge Combs Greene made a similar statement in footnote 6 of the Omnibus Order: “Dr. Zimmet does not, in his deposition, states [sic] that he believes the sewage was the actual source of the
Le-gionella
bacteria. Rather, ... he ‘believes’ the apartment complex was the most likely source” (bold font in the original).
Russell is correct that his burden was to prove the “most likely” source of his exposure.
See Snyder v. George Washington Univ.,
890 A.2d 237, 248 (D.C.2006) (“We require only that a causation expert state an opinion, based on a reasonable degree of medical certainty, that the defendant’s conduct was a likely cause of the plaintiffs injuries.”). Because it is not clear to us what Judge Combs Greene intended to
convey through her emphasis on the words “believes,” “actual,” and “most likely,”
we are skeptical of Russell’s claim that she misapprehended the legal standard or incorrectly applied it. We are, however, satisfied that even if Judge Combs Greene erroneously held Russell to a heightened standard of proof, the basis for her ruling that Dr. Zimmet was not qualified to testify as an expert on causation was that Dr. Zimmet did not provide “any real basis (based on facts or science) for his opinions.” That was a sufficient basis for precluding him from testifying as a causation expert regardless of the degree of certainty that was required. For that and all the foregoing reasons, we will not disturb Judge Combs Greene’s ruling on the motion
in limine.
Russell argues in the alternative that Dr. Zimmet was entitled to testify about the source of Russell’s exposure to
Legionella
as a fact witness rather than as an expert witness. It is true that “[i]nso-far as a physician obtains and develops his information and opinions in the course of his treatment of a patient, he becomes an ‘actor or viewer’ who should be treated as an ordinary witness rather than as an expert covered under Rule 26(b)(4).”
Adkins v. Morton,
494 A.2d 652, 657 (D.C. 1985) (explaining that “the crucial inquiry is whether the facts and opinions possessed by the expert were obtained for the specific purpose of preparing for the litigation in question”);
Gubbins v. Hurson,
885 A.2d 269, 277 (D.C.2005) (quoting
Adkins
and reasoning that “Dr. Kelly’s opinion, which he expressed to Gubbins while she still was under his care, that her nerves were injured by the medication she received during her surgery” “clearly fell within this ‘exempt-from-Rule 26(b)(4)’ category”).
However, “a witness may be an ‘expert’ as to some matters and an ‘actor’ as to others.”
Id.
(internal quotation marks omitted). The question here is one of timing: When did Dr. Zimmet reach the opinions about which Russell sought to have him opine? If he reached them only “while preparing for his trial appearance[,]”
id.
at 278, he needed to be qualified as an expert to be permitted to testify.
What the record reveals is the following: Dr. Zimmet testified that he had formulated his opinions as of February 5, 2018 (the date of Russell’s previous Rule 26(b)(4) statement). There was evidence that, as recently as September 2012, Dr. Zimmet or (much more frequently) his staff had provided care to Russell in connection with a blood clot in his leg that stemmed from his being bedridden for weeks while recovering from Legionnaires’ disease. However, Russell testified that the last time he went to
any
doctor for anything relating to the Legionnaires’ disease itself was in June 2011. In addition, Dr. Zimmet testified that Russell’s diagnosis of Legionnaires’ disease was made by other doctors prior to Dr. Zimmet’s involvement in Russell’s treatment, and one of those doctors (“the infectious disease doctor”) wrote in
the medical records (apparently incorrectly) that Russell reported that he had water leakage in his apartment from a ventilation system and attributed the
Legionella
exposure to that.
Dr. Zimmet described the “grilling” about “[w]hat’s your exposure” that “we” doctors conduct when encountering a patient who has Legionnaires’ disease, but also explained that Russell was asked about exposures “at the time he came in the hospital in his May admission,” clarified that Russell did not answer such questions to Zimmet specifically, and acknowledged he had never “had the responsibility for determining the source of an individual’s
Legionella
bacterial exposure as part of [his] clinical practice.” Further, Dr. Zimmet had never visited the Fitch Street apartment building. He relied on what he read in Russell’s deposition transcript and other depositions and on what he saw in the video of Apartment 1 for his knowledge of the conditions that existed in the building, and, importantly, he did not see the video or any photos of Apartment 1 until the day of his deposition, which was April 19, 2013.
In short, the record provides no foundation for a conclusion that Dr. Zimmet “formulated the opinions in question while he was treating” Russell,
Gubbins,
885 A.2d at 278, rather than in preparation for his deposition and for trial, such that it was error not to permit him to present the opinions as a fact witness.
IV. Summary Judgment
Russell’s final contention is that he presented sufficient circumstantial evidence for a reasonable jury to fairly infer that
Legionella
bacteria were present in his apartment building and that he was exposed to the bacteria there. He argues that whether sewer water is a hospitable breeding ground for
Legionella
is a disputed issue that could not be resolved on summary judgment. We can agree with the latter contention, but the problem for Russell, who bore the burden of proof, was that, upon the court’s ruling on the motion
in limine,
he was left without an expert to testify that sewage-contaminated water likely contains a strain or strains of
Le-gionella
associated with Legionnaires’ disease and that Russell’s exposure to sewage-contaminated water was the likely source of his illness. Russell needed to prove more than the “bare possibility” that the contaminated water in the apartment building was the exposure source.
Ferrell,
691 A.2d at 650.
Meanwhile, Call/D’s environmental health expert John David Krause, whose affidavit describes his involvement in “at least 10 investigations involving Legionnaires’ disease” and cites his consideration of the “relevant peer-reviewed scientific literature,” was poised to testify that
“Le-gionella
are not normally found in sewage”; that
Legionella
generally “corn-
pete[] poorly with other bacteria in the environment[,]” which “typically out compete and may even prey upon
Legionella
and that “aerosols of water droplets, such as those created by showering, are capable of carrying
Legionella
bacteria[.]”
Call/ D’s expert Tim Keane, a water treatment consulting engineer who runs a company called
Legionella
Risk Management, Inc., and whose expert report describes his “lead role in
[Legionella
] outbreak investigations” for state and county health departments, was prepared to testify that 24% of Legionnaires’ outbreaks are associated with travel and that travel-related outbreaks are difficult to detect because of the dispersal of persons from the source of the outbreak; and that samples of stagnant water taken from Apartment 6, which Russell had vacated, in September 2011 were negative for Legionella,
In addition, Call/D’s expert Dr. Hung Cheung, a specialist in environmental medicine who had testified as an expert in epidemiology and toxicology, was poised to testify,
inter alia,
that Russell’s visit to Bryce Resort was consistent with the incubation period for Legionnaires’ disease.
Reviewing the matter
de novo,
we conclude that, presented with the foregoing and other testimony by Call/D’s experts and no expert causation testimony to the contrary,
a jury would have had no basis other than speculation for finding that sewage-contaminated water or sewage vapors at the apartment building were the source of Russell’s
Legionella
exposure.
Accordingly, Judge Combs Greene did not err in granting summary judgment in favor of Call/D.
For the foregoing reasons, the judgment of the trial court is
Affirmed.