In the Matter of the Worker's Compensation Claim of: Mary Leib v. State of Wyoming, ex rel., Department of Workforce Services, Workers' Compensation Division, 373 P.3d 420

Mary Leib, a groundskeeper at Laramie County Community College, developed bilateral breast abscesses after working with dirt mixed with untreated manure in 2012.
Initial cultures after incision and drainage grew peptostreptococcus organisms; she underwent two surgeries and returned to similar work between episodes.
Leib filed a workers’ compensation claim; the Division denied coverage, finding no workplace causation.
The contested case was heard by the Medical Commission, which credited the Division’s infectious disease expert (Dr. Dowell) over Leib’s treating/expert physician (Dr. Willis).
The Commission noted the manure/dirt pile was never tested, experts disputed causation, and concluded Leib failed to prove her injury arose out of employment by a preponderance of the evidence.
The district court affirmed the Commission; the Supreme Court of Wyoming affirmed, applying substantial-evidence and credibility deference to the Commission.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether Commission improperly raised burden by requiring identification/testing of bacteria in workplace	Leib: Commission effectively required proof to a medical-certainty level (identifying bacteria in the dirt/manure), which was unreasonable given changing material and delayed testing	Division: Commission permissibly relied on lack of testing plus expert opinion that organisms are common and not workplace-specific	Held: No error—Commission did not demand impossible proof; lack of testing and competing expert opinions supported denial under preponderance standard
Whether Commission gave undue weight to Division’s expert	Leib: Dowell misstated medical history and did not examine her, so his opinion was unreliable and should be discounted	Division: Dowell’s opinion rested on organism epidemiology and likelihood, not the miscited history; paper review is permitted; Commission may credit his board-certified expertise	Held: No error—Commission reasonably credited Dowell’s specialized testimony; misstatement did not taint his causation opinion

Murray v. State ex rel. Wyo. Workers’ Safety & Compensation Div., 993 P.2d 327 (Wyo. 1999) (temporal relationship can support causation but complex medical questions require expert proof)
Thornberg v. State ex rel. Wyoming Workers’ Compensation Division, 913 P.2d 863 (Wyo. 1996) (immediate, direct injuries may establish causation without medical evidence)
Stevens v. State ex rel. Dep’t of Workforce Servs., 338 P.3d 921 (Wyo. 2014) (claimant must show causal connection to a reasonable degree of medical probability)
Dale v. S & S Builders, LLC, 188 P.3d 554 (Wyo. 2008) (substantial-evidence standard for agency factfinding)
Leavitt v. State ex rel. Wyo. Workers’ Safety & Comp. Div., 307 P.3d 835 (Wyo. 2013) (deference to hearing examiner’s credibility determinations)