OPINION
By the Court,
These consolidated writ petitions raise two novel issues involving the admissibility of expert testimony: (1) whether a nurse can testify as an expert regarding medical causation, and (2) whether defense expert testimony offering alternative causation theories must meet the “reasonable degree of medical probability” standard set forth in
Morsicato v. Sav-On Drug Stores, Inc.,
Here, in Docket No. 56928, we conclude that the district court abused its discretion when it allowed an unqualified nurse to offer expert testimony regarding medical causation; however, it did not abuse its discretion when it determined that one of the defense’s other expert witnesses could offer testimony regarding alternative causation theories. In Docket No. 57079, we conclude that the district court abused its discretion when it precluded the same nurse from offering any expert testimony because a nurse can testify within his or her area of expertise but not as to causation, unless he or she possesses the requisite knowledge, skill, experience, or training to identify cause. 2 Therefore, writ relief is granted in part and denied in part.
FACTS
These writ petitions arise out of two separate actions resulting from an outbreak of hepatitis C at the Endoscopy Clinic of Southern Nevada (ECSN) in Las Vegas. The defendants in the district court are companies involved in the pharmaceutical industry that are being sued by former patients who were allegedly infected with hepatitis C while having procedures performed at ECSN and their spouses.
In each case below, the plaintiffs are suing the defendants for strict products liability, including design defect, failure to warn, and breach of implied warranty of fitness for a particular purpose. The plaintiffs 3 theorize that defective vials of the anesthetic Propofol caused them to contract hepatitis C. They claim that defendants Baxter Healthcare Corporation; Sicor, Inc.; Teva Parenteral Medicines, Inc., f.k.a. Sicor Pharmaceuticals, Inc.; and McKesson Medical-Surgical, Inc. (collectively, Sicor), are liable for their distribution of 50mL vials of Propofol to endoscopy clinics because that size vial lends itself to reuse and contamination. More specifically, the plaintiffs allege that medical personnel at ECSN injected needles contaminated with hepatitis into vials of Propofol. The medical personnel then allegedly reused those vials and injected the plaintiffs with the now-contaminated Propofol.
*523 To rebut these claims, Sicor obtained opinions from several experts, including the two who are at issue in this appeal: David Hambrick, a registered nurse, and Jonathan Cohen, M.D., a professor of medicine. In both cases, these experts opined that improper cleaning and disinfection techniques at the clinic may have caused the plaintiffs to contract hepatitis C, but they could not identify a specific piece of equipment that transmitted the virus. The Williams Petitioners refer to this theory as the “dirty scopes” theory. Based on those opinions, the plaintiffs in each case filed motions in limine to exclude Nurse Hambrick’s and Dr. Cohen’s testimony. However, the district courts hearing these two cases came to different conclusions concerning Nurse Hambrick.
Docket No. 56928
The Williams Petitioners filed two motions in limine to exclude expert testimony. In the first motion, the Williams Petitioners asked the district court to preclude Sicor from offering testimony that “dirty scopes” caused their hepatitis C because Dr. Cohen and Nurse Hambrick “did not have an opinion to a reasonable degree of medical probability that a ‘dirty scope’ was the cause of hepatitis ...” In the second motion, the Williams Petitioners similarly asked the district court to preclude the defendants from offering testimony regarding a “dirty scope” alternative theory of causation, and they also argued that nurses cannot give testimony regarding causation. At the hearing on the motions, the Williams Petitioners again argued that Nurse Hambrick could not qualify as an expert.
The district court denied both motions for two reasons. First, the court noted that “NRS 632.019 does not preclude a nurse from providing expert testimony.”
4
The district court cited
Staccato v. Valley Hospital,
Docket No. 57079
The Pagan Parties filed a similar motion in limine to exclude testimony regarding a “dirty scope” theory. Unlike in the Williams *524 Petitioners’ case, the district court granted the Pagan Parties’ motion to exclude Nurse Hambrick from offering his opinion that unsafe cleaning practices caused the plaintiffs to contract hepatitis C. The district court found that Nurse Hambrick’s opinion was related to a specific alternative causation theory and, therefore, had to meet the reasonable degree of medical probability standard announced in Morsicato. Applying this standard, the district court determined that, based on Nurse Hambrick’s deposition testimony, he could not testify to greater than a 10-percent probability that the cleaning processes used caused the plaintiffs’ hepatitis, and Mor-sicato requires greater than 50 percent. The district court also found that, pursuant to Morsicato, an “expert can not simultaneously testify as to 2 different medical causation opinions,” and, here, Nurse Hambrick could not identify a specific piece of equipment as the cause of the plaintiffs’ hepatitis C.
After the district courts entered their respective orders regarding Sicor’s expert witnesses, the aggrieved parties (the Williams Petitioners in their case and Sicor in the Pagan Parties’ matter) petitioned this court for extraordinary writ relief. On October 14 and November 4, 2010, this court granted temporary stay orders in the underlying matters pending the resolution of the writ petitions. The November 4 order also consolidated these two original writ proceedings.
DISCUSSION
When a writ of mandamus is appropriate
“A
writ of mandamus is available to compel the performance of an act that the law requires as a duty resulting from an office, trust, or station or to control an arbitrary or capricious exercise of discretion.”
International Game Tech. v. Dist. Ct.,
Despite these limitations, we recognize some narrow exceptions when writ relief is appropriate concerning challenges to decisions that admit or exclude evidence. We acknowledge that the ability to
*525
appeal a final judgment may not always constitute an adequate and speedy remedy that precludes writ relief, depending on the “underlying proceedings’ status, the types of issues raised in the writ petition, and whether a future appeal will permit this court to meaningfully review the issues presented.”
D.R. Horton v. Dist. Ct.,
We conclude that an exception to our normal rule rejecting writ petitions challenging evidentiary rulings is necessary in this matter, and we exercise our discretion to consider these writ petitions. These petitions involve issues of first impression regarding whether a nurse can offer expert testimony about medical causation and the appropriate standard for defense expert testimony regarding alternative theories of medical causation, and these issues have the potential of being repeated in the many endoscopy cases pending before the district court. We also conclude that, in this narrow instance, waiting for an appeal to resolve these issues does not provide the parties with an adequate or speedy remedy because the ongoing litigation of multiple cases in the district court and conflicts in evidentiary rulings limits our ability to meaningfully review the issues on appeal. We reemphasize, however, that generally this court will not consider writ petitions challenging evidentiary rulings, as those rulings are discretionary and there typically is an adequate remedy in the form of an appeal following an adverse final judgment. However, in the interest of judicial economy, it is necessary to resolve the issues presented in these writs.
Standard of review
In the context of a writ petition, this court gives deference to the district court’s findings of fact, but reviews questions of law de novo.
Gonski
v.
Dist. Ct.,
Admissibility of Nurse Hambrick’s and Dr. Cohen’s testimony
An “expert witness assessment turns on whether the proposed witness’s special knowledge, skill, experience, training, or education will assist the jury.”
Staccato,
(1) he or she [is] qualified in an area of “scientific, technical or other specialized knowledge” (the qualification requirement); (2) his or her specialized knowledge must “assist the trier of fact to understand the evidence or to determine a fact in issue” (the assistance requirement); and (3) his or her testimony must be limited “to matters within the scope of [his or her specialized] knowledge” (the limited scope requirement).
Hallmark
v.
Eldridge,
Nurse Hambrick is not qualified to testify as to medical causation
The Williams Petitioners and the Pagan Parties make two arguments regarding Nurse Hambrick’s qualifications to testify as to medical causation. First, they argue that nurses can never testify as to medical causation because NRS 632.019 defines “[registered nurse” as “a person who is licensed to practice professional nursing,” and NRS 632.018 provides that professional nursing “does not include acts of medical diagnosis.” Thus, they argue, nurses are not qualified to render expert opinions regarding causation. They ask us to adopt what they characterize as a ‘ ‘near universal rule that a nurse can not play doctor and give medical causation testimony.” Second, they challenge whether Nurse Hambrick possesses the requisite skill, knowledge, experience, training, or education to testify to the cause of the hepatitis C transmission that occurred at ECSN. We disagree that nurses are per se precluded from testifying as to medical causation, but we agree that Nurse Hambrick did not meet the requirements to testify as an expert regarding medical causation here.
*527
In
Staccato,
we recognized that “in accordance with Nevada’s statutory scheme governing expert witness testimony, and in furtherance of sound public policy, the proper measure for evaluating whether a witness can testify as an expert is whether that witness possesses the skill, knowledge, or experience necessary to [testify].”
In some circumstances, a nurse may obtain the requisite skill, knowledge, or experience to testify as to cause.
See Maloney v. Wake Hospital Systems, Inc.,
Nurse Hambrick has extensive experience in cleaning and disinfecting the type of equipment used during an endoscopy procedure. He is a registered nurse in Texas, has been certified in gas-troenterology for ten years, and he is currently the manager of the gastroenterology lab at the Methodist Dallas Medical Center. He has also been published in a peer-reviewed journal regarding biopsy and tissue acquisition equipment, has written and spoken extensively on the topic of infection control, and has trained over 75 people on proper disinfection techniques. Additionally, he served as director of the national board of directors for the Society of Gastroenterology Nurses and Associates. Nurse Hambrick’s educational experience includes a two-year nursing degree, and he was due to complete a bachelor of science in nursing in December 2010. Both the Williams Petitioners and the Pagan Parties argue that these facts do not make Nurse Hambrick qualified to testify as an expert because he does not a have a four-year college degree, and his experience with endoscopy equipment cleaning and disinfectant techniques is insufficient to qualify him to give medical causation opinions. The Williams Petitioners also argue that Nurse Hambrick’s lack of knowledge about the hepatitis C virus demonstrates that he is unqualified as a medical expert.
Despite his experience with endoscopy equipment and disinfectant techniques, Nurse Hambrick has little, if any, experience in diagnosing the cause of hepatitis C. Nurse Hambrick never indicated, and Sicor did not contend, that Nurse Hambrick ever made medical diagnoses to assess cause. In fact, Nurse Hambrick noted that in his previous nursing positions, doctors, not nurses, always determined the cause of illnesses indicated on a patient’s chart. Also, by Sicor’s own admission, Nurse Hambrick is only a leading expert on “endoscopic reprocessing” and “the standards gov *529 erning and proper means of disinfecting gastrointestinal endoscopy equipment.” This does not, by extension, qualify him to testify regarding medical causation. We thus conclude that, while Nurse Hambrick may be more than qualified to testify as to proper cleaning and sterilization procedures for endoscopic equipment and can testify on those subjects, he does not possess the requisite skill, knowledge, or experience to testify as an expert witness regarding the medical cause of hepatitis C transmission at ECSN. 7
Dr. Cohen will assist the trier of fact
To assist the trier of fact, medical expert testimony regarding causation must be “made to a reasonable degree of medical probability.”
Morsicato v. Sav-On Drug Stores, Inc.,
Sicor argues that, in light of the plaintiff’s burden of proving causation in a products liability action,
Rivera
v.
Philip Morris, Inc.,
Once the plaintiff has demonstrated a prima facie case and met his or her burden, the defendant can traverse the plaintiff’s case in three ways.
See id.
The defendant may (1) cross-examine the plaintiff’s expert, (2) contradict the expert’s testimony with his own expert, and/or (3) propose an independent alternative causation theory.
Id.
If the defendant chooses the third approach, his or her expert’s testimony is subject to the reasonable degree of medical probability standard because, in order to assist the trier of fact, testimony establishing cause must meet a heightened threshold requirement.
Id.
at 538;
see also Goudreault v. Kleeman,
However, if the defense expert’s testimony is used for the purpose of cross-examining the plaintiff’s expert or to otherwise contradict the plaintiff’s causation theory by comparing that theory to other plausible causes, the defense expert does not need to state each additional cause to a greater-than-50-percent probability.
8
Stinson,
In
Wilder
v.
Eberhart,
We agree with the Wilder court’s holding, and it logically comports with our conclusion that when a defense expert’s testimony is used to contradict a plaintiff’s causation theory by comparing that theory to other plausible causes, each additional cause does not need to be stated to a greater-than-50-percent probability. To hold otherwise would severely hinder a defendant’s ability to undermine the causation element of the plaintiff’s case and could result in an unfair shifting of the burden of proof to the defendant. As illustrated by the Wilder court,
if ninety-nine out of one hundred medical experts agreed that there were four equally possible causes of a certain injury, A, B, C and D, and plaintiff produces the one expert who conclusively states that A was the certain cause of his injury, defendant would be precluded from presenting the testimony of any of the other ninety-nine experts, unless they would testify conclusively that B, C, or D was the cause of injury. Even if all of defendant’s experts were prepared to testify that any of the possible causes A, B, C or D, could have equally caused plaintiff’s injury, so long as none would be prepared to state that one particular cause, other than that professed by plaintiff more probably than not caused plaintiff’s injury, then defendant’s experts would not be able to testify at all as to causation. We think that such a result . . . would be manifestly unjust and unduly burdensome on defendants.
Although we recognize a lower standard for rebuttal expert testimony regarding medical causation, any alternative causation theories proffered by a defense expert to controvert the plaintiff’s theory of cause are still subject to certain threshold requirements, namely that medical experts testifying as to cause must avoid speculation.
See Morsicato,
Accordingly, for the reasons set forth above, we grant in part and deny in part the Williams Petitioners’ petition for extraordinary writ relief and direct the clerk of this court to issue a writ of mandamus in Docket No. 56928 instructing the district court to set aside that portion of its order allowing Nurse Hambrick to testify as to medical causation. We further grant in part and deny in part Sicor’s petition for extraordinary writ relief and direct the clerk of this court to issue a writ of mandamus in Docket No. 57079 instructing the district court to set aside that portion of its order excluding Nurse Hambrick from testifying as an expert witness on the subjects of proper cleaning and sterilization procedures for endoscopic equipment. Nurse Hambrick may testify within his area of expertise; however, because we conclude he does not possess the requisite qualifications, he may not testify as to medical causation. 9
Notes
The district court in Docket No. 57079 did not address the admissibility of Dr. Cohen’s testimony regarding causation.
In Docket No. 56928, the plaintiffs in the lower court and petitioners here are James M. and Heidi Williams, and Joanne and Kenneth G. Allen. Heidi and Kenneth are suing in their capacity as spouses of James and Joanne, who underwent procedures at ECSN. We collectively refer to them as the Williams Petitioners. In Docket No. 57079, the plaintiffs in the lower court and the real parties in interest here are Maria Pagan and William I. and Marilyn Elaine Bil-ger. Marilyn is suing in her capacity as William’s spouse. We collectively refer to them as the Pagan Parties.
NRS 632.019 is the statutory definition of “[Registered nurse.”
We recognize that some jurisdictions have adopted bright-line standards holding that, while nurses are qualified to give opinions related to standard of care, they are not similarly qualified to make medical diagnoses or opine as to medical causation.
See Phillips
v.
Alamed Co., Inc.,
Just as a licensed professional may gain experience beyond the scope of his or her license,
see Staccato
v.
Valley
Hospital,
Because we conclude that Nurse Hambrick is not qualified to offer testimony regarding medical causation, we do not analyze the assistance requirement as it pertains to him.
By definition, probability requires more than 50-percent likelihood.
Stinson
v.
England,
We vacate the stays of these cases issued on October 14 and November 4, 2010.
