United States Court of Appeals
                          FOR THE EIGHTH CIRCUIT
                                  ___________

                                  No. 07-3010
                                  ___________

Racheal L. Bland,                    *
                                     *
            Appellant,               *
                                     * Appeal from the United States
     v.                              * District Court for the
                                     * Southern District of Iowa.
Verizon Wireless, (VAW) L.L.C.;      *
Cellco Partnership; Christopher      *
Michael Reid,                        *
                                     *
            Appellees.               *
                                ___________

                            Submitted: May 12, 2008
                               Filed: August 14, 2008
                                 ___________

Before RILEY, BOWMAN, and HANSEN, Circuit Judges.
                           ___________

RILEY, Circuit Judge.

       Racheal Bland (Bland) brings this action claiming she ingested freon after a
Verizon Wireless, (VAW) L.L.C. (Verizon) employee sprayed canned air containing
freon into her water bottle. Bland contends ingesting the freon caused her to suffer
exercise-induced asthma. The district court1 excluded evidence from Dr. Nancy


      1
      The Honorable Celeste F. Bremer, United States Magistrate Judge for the
Southern District of Iowa, to whom the case was referred for final disposition by
consent of the parties pursuant to 28 U.S.C. § 636(c).
Sprince (Dr. Sprince), Bland’s treating physician, opining the freon caused Bland’s
exercise-induced asthma. The district court then granted defendants’ motion for
summary judgment because, without Dr. Sprince’s testimony, Bland was unable to set
forth sufficient evidence of causation. Bland appeals. We affirm.

I.     BACKGROUND
       On June 8, 2005, Bland and her friend J.J. Roetlin (Roetlin) entered a Verizon
store in Coralville, Iowa, so Roetlin could have his phone updated. When they left the
store, Bland inadvertently left her water bottle behind. After Bland and Roetlin left,
Verizon employee Christopher Reid (Reid) sprayed compressed air into Bland’s water
bottle “as a joke,” believing the water bottle belonged to a fellow Verizon employee.
The compressed air would freeze the top of the water in the water bottle, which
supposedly was funny. Reid previously performed this same “joke” with his own
water bottle and the water bottles of fellow employees. Once Reid drank the water in
a bottle after such a “joke” and experienced no ill effects. No one else reported any
adverse effects from drinking the water frozen in the bottles.

       Shortly after Reid sprayed the compressed air into Bland’s water bottle, Roetlin
returned and retrieved Bland’s water bottle from a Verizon employee. Several Verizon
employees were laughing as Roetlin took the bottle, causing Roetlin to ask, “Is
something funny? Did you piss in [the bottle] or something?” None of the Verizon
employees responded and Roetlin left saying, “Take it easy.” Though the Verizon
employees never acknowledged taking any action, Roetlin jokingly reported to Bland,
“I wouldn’t drink that [because when I retrieved the bottle] they were laughing pretty
hard . . . . Maybe they peed in it.”

       Neither Bland nor Roetlin attempted to open the water bottle or drink from it
until after they drove to Roetlin’s home to make dinner, a drive of 30 to 45 minutes.
At Roetlin’s home, Bland opened the bottle which “made a—kind of pressurized
noise.” Bland thought this sound was weird but figured it may have been caused by

                                         -2-
the heat. Bland took a drink, then decided to smell the contents “because [she] thought
it was odd that [the bottle] was pressurized,” even though she “didn’t know if it was
going to stink from being in the heat or what.” Bland took a big whiff and the bottle
“had a really potent smell that made me cough.” Bland “took another drink and kind
of swished it around [her] mouth . . . trying to figure out if there was something in there
or if [she] was just being crazy.” In total, Bland had “two or three drinks at most.”
Bland then passed the bottle to Roetlin saying, “Smell this, it smells like plastic.”

       Bland later reported to her doctor, “Immediately after drinking from the bottle
she coughed a few times, and this coughing persisted for nearly an hour.” Bland also
described a “sore sensation in her throat” and for the next few days a “raspy sensation
in her lungs.” Bland developed a headache which persisted for about two weeks.

       Roetlin also took a drink from the bottle but did not swallow. Both Bland and
Roetlin reported not feeling well. They called the police. The police spoke to Reid,
who admitted spraying compressed air2 in Bland’s water bottle. Roetlin and Bland
delivered the bottle to the University of Iowa Hygienic Lab (Lab) for testing. The Lab
determined the bottle contained 820 parts per million (ppm) (.08%) of difluoroethane,
a freon compound. The Lab then contacted the Iowa Poison Control Center (Poison
Control) to determine what the Lab should tell Roetlin and Bland. After consulting
Poison Control, the Lab contacted Roetlin and referred Bland and Roetlin “to a
physician if experiencing symptoms.”




      2
        The compressed air at Verizon was called “Dust Blaster” and contained
tetrafluoroethane. The compound detected in the Bland water bottle contents was
difluoroethane. The mass spectrum analysis of tetrafluoroethane and the mass
spectrum analysis of difluoroethane are not the same (four fluoro molecules vs. two
fluoro molecules). The testing Lab had no explanation for why the water in Bland’s
bottle would contain difluoroethane if the canned air contained tetrafluoroethane and
not difluoroethane.

                                           -3-
       On July 13, 2005, Bland was seen by Dr. Sprince for the first time, complaining
of shortness of breath when running. Bland’s lung function test results were normal.
Dr. Sprince initially thought Bland’s shortness of breath might be due to lack of
physical conditioning, change in her exercise routine or the July weather. Dr. Sprince
eventually diagnosed Bland as having “exercise-induced asthma.” Dr. Sprince
theorized that “[b]ased on the initial clinical findings, [a] strong temporal relationship
between the inhalation of Freon and the occurrence of respiratory symptoms, and the
subsequent response to pre-exercise treatment with inhaled bronchodilator” that
Bland’s exercise-induced asthma was caused by the inhalation of freon.

      Bland filed this action in the Iowa District Court for Johnson County on January
5, 2006. Verizon removed this action to federal court on January 26, 2006. Bland was
granted leave to amend to add Cellco Partnership and Reid as defendants. All
defendants moved for summary judgment on May 21, 2007.

      Bland sought to have the testimony of her treating physician, Dr. Sprince,
admitted to establish a causal link between Bland’s inhalation of freon and Bland’s
exercise-induced asthma. The district court excluded Dr. Sprince’s testimony because
Dr. Sprince’s proferred testimony as to causation did not satisfy the standards for
admission of expert scientific testimony under Daubert.3

II.   DISCUSSION
      “We review for abuse of discretion rulings concerning the admissibility of
testimony that is offered as expert opinion.” Ahlberg v. Chrysler Corp., 

,
635 (8th Cir. 2007) (citing Hickerson v. Pride Mobility Prods. Corp., 

,
1256 (8th Cir. 2006)). We will not reverse a district court’s ruling on the admissibility
of evidence “absent a clear and prejudicial abuse of discretion.” 

(quoting
Pittman v. Frazier, 

, 989 (8th Cir. 1997)).


      3
       Daubert v. Merrell Dow Pharm., Inc., 

(1993).

                                           -4-
      Federal Rule of Evidence 702 provides:

      If scientific, technical, or other specialized knowledge will assist the trier
      of fact to understand the evidence or to determine a fact in issue, a
      witness qualified as an expert by knowledge, skill, experience, training,
      or education, may testify thereto in the form of an opinion or otherwise,
      if (1) the testimony is based upon sufficient facts or data, (2) the
      testimony is the product of reliable principles and methods, and (3) the
      witness has applied the principles and methods reliably to the facts of the
      case.

        “A trial judge must make a preliminary assessment of whether the proffered
expert’s methodology is both scientifically valid and applicable to the case.” 

(citing 

). “Under Rule 702, as amplified
by Daubert, factors bearing upon this determination include whether the expert’s
theory or technique (1) can be and has been tested, (2) has been subjected to peer
review and publication, (3) has a known or potential rate of error, and (4) has gained
general acceptance in the relevant community.” 

509 U.S. at 593-
94). “This ‘gatekeeping requirement’ is to ensure that the proffered expert exercises
the same ‘intellectual rigor’ in the courtroom as does an expert in the relevant field.”

Tire Co. v. Carmichael, 

, 152 (1999)).

        Bland sought to have the testimony of her treating physician, Dr. Sprince,
admitted to establish a causal link between Bland’s inhalation of freon and Bland’s
exercise-induced asthma. “A treating physician’s expert opinion on causation is subject
to the same standards of scientific reliability that govern the expert opinions of
physicians hired solely for purposes of litigation.” Turner v. Iowa Fire Equip. Co., 

, 1207 (8th Cir. 2000) (citing Kumho 

). The district
court excluded Dr. Sprince’s causation testimony because Dr. Sprince (1) failed
scientifically to eliminate other possible causes as part of her differential diagnosis;
(2) did not know “what amount of exposure to [the] difluroethane-containing Freon
causes, or involves an appreciable risk of causing, asthma”; (3) “had no good grounds

                                           -5-
for determining whether Bland was exposed to a sufficient dose of difluoroethane-
containing Freon to have caused her asthma, because [Dr. Sprince] . . . could not
determine or estimate the amount of difluoroethane or Freon . . . Bland was actually or
probably exposed [to] when she smelled the water in her water bottle”; (4) could not
extrapolate from the existing data because the gap between the data identified and Dr.
Sprince’s proferred opinion was “‘simply too great an analytical gap’ . . . to support
admissibility (quoting General Elec. Co. v. Joiner, 

, 146 (1997)) (citation
omitted)”; (5) did not offer as evidence any personal experience with “treating other
patients following a similar exposure to difluoroethane, Freon, or Freon with
difluoroethane”; and (6) reliance on temporal proximity, without more, is insufficient
to establish causation.

        Bland asserts the district court abused its discretion in holding Dr. Sprince’s
causation opinion was scientifically unsupported because the opinion was the product
of reliable methods and principles. Further, Bland asserts the district court “abused [its]
discretion by imposing a burden of proof tantamount to scientific certainty rather than
the preponderance of evidence standard required by law.”

             1.      Differential Diagnosis
       Bland asserts Dr. Sprince conducted a differential diagnosis which supports Dr.
Sprince’s causation opinion. We have held, “a medical opinion about causation, based
upon a proper differential diagnosis is sufficiently reliable to satisfy Daubert.” 

. A “differential diagnosis [is] a technique that identifies the cause of
a medical condition by eliminating the likely causes until the most probable cause is
isolated.” 

v. Gislaved Gummi AB, 

, 262 (4th Cir.
1999)). Dr. Sprince’s attempt to use a differential diagnosis to establish the inhalation
or ingestion of freon caused Bland’s exercise-induced asthma fails because Dr.
Sprince’s own testimony acknowledged the cause of exercise-induced asthma in the
majority of cases is unknown. Where the cause of the condition is unknown in the
majority of cases, Dr. Sprince cannot properly conclude, based upon a differential

                                           -6-
diagnosis, Bland’s exposure to freon was “the most probable cause” of Bland’s
exercise-induced asthma. As a practical matter, Dr. Sprince’s causation opinion could
not possibly be based upon a reasonable degree of medical certainty.

       The district court further concluded Dr. Sprince failed to eliminate scientifically
other possible causes as part of her differential diagnosis. Even if Dr.Sprince were able
to link exercise-induced asthma to freon inhalation or ingestion, Dr. Sprince must also
rule out other possible causes. 

(recognizing “an expert must ‘rule in’ the
suspected cause as well as ‘rule out’ other possible causes” (citing Nat’l Bank of
Commerce of El Dorado v. Associated Milk Producers, Inc., 

, 963
(E.D. Ark. 1998), aff’d, 

(8th Cir. 1999))). Dr. Sprince appears to have
focused on the temporal link between Bland’s exposure to the freon and the subsequent
diagnosis of exercise-induced asthma. It does not appear Dr. Sprince ever conducted
an investigation or analysis of Bland’s home or other environments to determine other
possible causes of Bland’s exercise-induced asthma. See Marmo v. Tyson Fresh Meats,
Inc., 

, 758 (8th Cir. 2006) (holding the district court acted within its
discretion in excluding the testimony of a toxicologist on medical causation where the
toxicologist did not exclude confounding factors leaving open the possibility of
competing causes). Where the majority of cases of exercise-induced asthma have no
known cause, and where Dr. Sprince failed to do an investigation and analysis of
Bland’s home or other environments in search of other possible causes, the district court
did not abuse its considerable discretion in determining Dr. Sprince’s differential
diagnosis did not satisfy Daubert.

              2.     Lack of Data
       The district court’s decision to exclude Dr. Sprince’s causation opinion is also
supported by Dr. Sprince’s lack of knowledge as to (1) “what amount of exposure to
[the] difluoroethane-containing Freon causes, or involves an appreciable risk of causing,
asthma”; and (2) what amount of difluoroethane-containing freon “Bland was actually
or probably exposed [to] when she smelled the water in her water bottle.” “Critical to

                                           -7-
a determination of causation is characterizing exposure.” Federal Judicial Center, The
Reference Manual on Scientific Evidence 472 (2d ed. 2000). “The magnitude or
concentration of an exposure should be estimated” and “[t]he temporal aspects of the
exposure should be determined—whether the exposure was short-term and lasting a few
minutes, days, weeks, or months, or was long-term and lasted for years.” 

lacked knowledge regarding what level of exposure to freon constitutes an
appreciable risk of causing asthma and the specific concentration and degree of Bland’s
exposure to the freon. Without knowledge of these data points, Dr. Sprince could not
extrapolate from the existing data because, as the district court reasoned, the gap
between the data identified and Dr. Sprince’s proferred opinion was “‘simply too great
an analytical gap’ . . . to support admissibility.” (quoting General Elec., 

).

       Lacking data regarding (1) what exposure levels would involve an appreciable
risk of asthma, and (2) Bland’s actual exposure level, the district court then looked for
other evidence which would support Dr. Sprince’s causation opinion. The court
suggested one way in which Dr. Sprince may have been able to buttress her opinion
would be offering as evidence any personal experience with treating other patients
following a similar exposure to difluoroethane, freon, or freon with difluoroethane.
When asked about her personal experience treating other patients with similar exposure,
Dr. Sprince admitted she had no such experience. See Kumho Tire, 

(explaining experience-based testimony requires court scrutiny to determine whether
the “same level of intellectual rigor” was employed).

      The only remaining basis for Dr. Sprince’s causation opinion is temporal
proximity, that is, Bland’s inhalation or ingestion of the contents of the water bottle
occurred shortly before Bland was diagnosed with exercise-induced asthma. “In the
absence of an established scientific connection between exposure and illness, or
compelling circumstances . . . the temporal connection between exposure to chemicals
and an onset of symptoms, standing alone, is entitled to little weight in determining

                                          -8-
causation.” Moore v. Ashland Chem., Inc., 

, 278 (5th Cir.1998) (footnote
reference omitted). “Under some circumstances, a strong temporal connection is
powerful evidence of causation.” Bonner v. ISP Techs., 

, 931 (8th Cir.
2001) (citation omitted). “[I]f a person were doused with chemical X and immediately
thereafter developed symptom Y, the need for published literature showing a correlation
between the two may be lessened.” 

v. Shaw Indus., Inc., 

, 154 (3d Cir. 1999)). The temporal relationship often will be only one of several
factors, and the weight to be given to the temporal relationship “will differ depending
on the strength of that relationship.” 

. Here, the district court
properly discounted all the other factors supporting Dr. Sprince’s opinion Bland’s
exposure to freon caused Bland’s exercise-induced asthma leaving only temporal
proximity to support Dr. Sprince’s causation opinion. Even though the Lab suggested
Bland go to the doctor if she had symptoms, Bland did not make an appointment with
a doctor until two to three weeks after the incident, and did not visit a doctor until
consulting Dr. Sprince on July 13, 2005, five weeks after the incident. Where the sole
support for Dr. Sprince’s causation opinion is the temporal connection, the five week
delay between Bland’s exposure to the freon and Bland’s visiting a doctor, with a
subsequent diagnosis of exercise-induced asthma, is insufficient to support Dr.
Sprince’s causation opinion. The district court did not abuse its broad discretion in
excluding Dr. Sprince’s causation testimony.

III.     CONCLUSION
       Having determined the district court’s decision to exclude the causation testimony
of Dr. Sprince was not an abuse of discretion, we conclude, under a de novo review, see
Green v. Franklin Nat’1 Bank of Minneapolis, 

, 910 (8th Cir. 2006), the
district court did not err in granting defendants’ motion for summary judgment because,
as a matter of law, Bland cannot establish causation without expert testimony. We
affirm.
                            _____________________________



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