No “Balance-Tipping” Presumption in Occupational Disease Claims: Clarified Burdens of Proof in Weeks v. Oneida County (Idaho 2025)

Introduction

In Weeks v. Oneida County, the Idaho Supreme Court affirmed an Industrial Commission decision denying workers’ compensation medical and death benefits arising from a COVID-19 fatality. The claimant, the Estate of William Weeks (through his widow, JaLyn Weeks), alleged that Mr. Weeks, a county road-and-bridge equipment operator, contracted COVID-19 at work in September 2021 and died of complications on October 9, 2021.

The appeal presented three principal issues:

Whether the Commission applied the wrong legal standard—effectively requiring proof “beyond every possible doubt”—instead of a preponderance of the evidence.
Whether the Commission erred by not resolving doubts in favor of compensability, as some accident cases suggest.
Whether the Commission ignored its own factual findings and reached an inconsistent conclusion, particularly regarding the likely window of infection and potential workplace transmission.

The Court’s opinion clarifies core principles governing occupational disease claims in Idaho, especially for infectious diseases like COVID-19, and draws a sharp doctrinal line between accident cases and occupational disease cases. The decision does not reach whether COVID-19 is, categorically, a compensable occupational disease under Idaho Code; rather, it resolves the case on causation.

Summary of the Opinion

The Idaho Supreme Court affirmed the Commission’s denial of benefits. It held that:

The Commission applied the correct burden of proof: the claimant must prove causation by a preponderance of the evidence, i.e., to a reasonable degree of medical probability. The Commission’s use of the word “impossible” reflected its assessment of the evidentiary record, not a higher legal standard.
The “resolve doubts in favor of the employee” articulation—used in accident/injury cases to determine whether an accident arose out of and in the course of employment—does not apply to occupational disease causation. Occupational disease claims remain subject to the claimant’s burden of proving that the disease was actually incurred in the employer’s employment to a probable (not merely possible) degree.
Substantial and competent evidence supports the Commission’s finding that Mr. Weeks did not more likely than not contract COVID-19 at work. The Commission permissibly credited the employer’s expert on incubation timing, rejected one alleged workplace exposure date as medically improbable, and found that non-work exposures could not be ruled out. The Court also rejected arguments premised on Mr. Weeks’s gas-station visits being within the course of employment because the Commission’s analysis already encompassed non-work-day and personal visits as alternative sources.
Because the claim failed on causation, the Court declined to decide whether COVID-19 qualifies as a compensable occupational disease under I.C. §§ 72-102(21)(a) and 72-438 (2021).

Analysis

Precedents Cited and Their Role

Evans v. Hara’s, Inc., 123 Idaho 473, 849 P.2d 934 (1993): Reaffirmed that the claimant bears the burden of proof by a preponderance of the evidence as to all facts essential to recovery. The Court relied on this baseline to evaluate whether the Commission applied the correct standard.
Jobe v. Dirne Clinic/Heritage Health, 163 Idaho 65, 408 P.3d 63 (2017) and I.C. § 72-439(1): An employer is not liable for an occupational disease unless the disease is actually incurred in the employer’s employment. The Court centered its analysis on this causation requirement.
Sundquist v. Precision Steel & Gypsum, Inc., 141 Idaho 450, 111 P.3d 135 (2005) and I.C. § 72-102(21)(a) (2021): Defined occupational disease as one due to the nature of the employment, characteristic of, and peculiar to the employment, not common to the general public (with the 2021 code cited). While the Court noted these elements, it did not reach them because causation failed.
Estate of Aikele v. City of Blackfoot, 160 Idaho 903, 382 P.3d 352 (2016) (superseded on other grounds) and Wichterman v. J.H. Kelly, Inc., 144 Idaho 138, 158 P.3d 301 (2007): Established that causation in occupational disease cases must be proven to a reasonable degree of medical probability, a standard the Court treats as interchangeable with preponderance in this context (see also Tenny v. Loomis Armored US, LLC, 168 Idaho 870, 489 P.3d 457 (2021) and Jensen v. City of Pocatello, 135 Idaho 406, 18 P.3d 211 (2000)).
Page v. McCain Foods, Inc., 141 Idaho 342, 109 P.3d 1084 (2005); Dinius v. Loving Care & More, Inc., 133 Idaho 572, 990 P.2d 738 (1999); Hansen v. Superior Products Co., 65 Idaho 457, 146 P.2d 335 (1944); and Jordan v. Walmart Assocs. Inc., 173 Idaho 115, 539 P.3d 593 (2023): Accident cases recognizing a liberal “resolve doubts” approach where there is uncertainty whether an accident occurred in the course of employment. The Court explicitly limited this principle to accidents, distinguishing it from occupational disease causation.
Roe v. Boise Grocery Co., 53 Idaho 82, 21 P.2d 910 (1933) and Koester v. State Insurance Fund, 124 Idaho 205, 858 P.2d 744 (1993) (tick-bite disease cases): The Court drew on these to show that occupational disease claims do not receive the “balance-tipping” presumption. In Koester, denial of benefits was affirmed where alternative sources of exposure could not be excluded—a parallel to Weeks. Roe did not support a presumption in favor of causation; rather, the work-related bite was independently supported and sufficient.
Lowery v. Galen Kuykendall Logging, 174 Idaho 922, 560 P.3d 1069 (2024); Hiatt v. Health Care Idaho Credit Union, 166 Idaho 286, 458 P.3d 155 (2020); Waters v. All Phase Constr., 156 Idaho 259, 322 P.3d 992 (2014): Reinforced the deferential substantial-evidence standard, the Commission’s role as fact-finder, and its prerogative to weigh competing medical opinions and resolve credibility.
Allen v. Partners in Healthcare, Inc., 170 Idaho 470, 512 P.3d 1093 (2022): The Court will set aside an order if the Commission misapplies the law; here, it found no misapplication.
Thompson v. Clear Springs Foods, Inc., 148 Idaho 697, 228 P.3d 378 (2010) (personal comfort doctrine) and Hansen v. Estate of Harvey, 119 Idaho 333, 806 P.2d 426 (1991) (going-and-coming rule): Cited by the claimant to argue gas-station stops were within the course of employment. The Court held the Commission had already encompassed non-employment-related stops and days-off visits as alternative sources, so no error.
Nelson v. Pocatello, 170 Idaho 160, 508 P.3d 1234 (2022): Mentioned to note a statutory supersession point in Aikele; not central to the outcome.

Legal Reasoning

The Court proceeded in four steps.

Burden of proof—preponderance/reasonable medical probability. The claimant must prove by a preponderance that the disease was actually incurred in the employer’s employment (I.C. § 72-439(1)), a standard synonymous with proof to a reasonable degree of medical probability in workers’ compensation medical causation. The Commission’s description of proof as “impossible” referred to the insufficiency of the evidence in the face of multiple plausible non-work exposures; it was not the imposition of a “beyond a reasonable doubt” or “beyond every possible doubt” burden.
No “resolve doubts in favor of the employee” presumption for occupational disease causation. The Court drew an analytical line between accident cases (where the “arising out of/in the course of” inquiry about the accident itself receives a liberal tilt) and occupational disease cases (which demand proof that the disease was actually incurred in the employment). Because diseases often develop over time and may arise from multiple potential exposures, the policy rationale for the accident presumption does not translate. The tick-bite cases (especially Koester) illustrate that where other plausible sources are not excluded, the claim fails. Applying this framework, the Commission properly required Weeks to demonstrate that a work exposure was more probable than non-work exposures.
Substantial evidence supported the Commission’s weighing of competing medical testimony. The Commission found the employer’s expert (Dr. Coffman) more persuasive on the timing of incubation and symptom onset:
- Typical symptom onset is three to five days after exposure, generally within seven days; it is not medically plausible to become symptomatic the day after exposure.
- Given Mr. Weeks’s symptom onset on September 29, exposures on September 23–26 were most consistent, and a September 28 exposure (when a sick co-worker returned) was rejected as medically improbable.
The Commission also found claimant’s expert (Dr. Nathan) premised his causation opinion on an assumption later contradicted by the record—namely, that Mr. Weeks had no non-work contacts. Evidence of a lumber store visit (September 18), frequent convenience-store stops, possible farm parts store visits, and potential contact with an uncle or neighbor on the ranch during the relevant period created multiple plausible non-work sources. In light of these “unknowns,” the Commission concluded a work-based source had not been shown to be more likely than not.
Gas-station visits and “course of employment.” Even assuming certain gas-station visits could be characterized as occurring in the course of employment under the personal comfort or going-and-coming doctrines, the Commission reasonably treated a wider field of non-employment visits—including off-days and personal trips—as alternative sources. Because causation failed on probabilities, the classification of any particular stop as “in course” did not alter the outcome.

Because the claim failed on causation, the Court declined to decide whether COVID-19 fits within Idaho’s occupational disease framework (I.C. §§ 72-102(21)(a), 72-438), leaving that question open.

Impact and Significance

Weeks materially clarifies Idaho law on occupational disease causation and the relationship between “liberal construction” and proof burdens.

No “balance-tipping” presumption for diseases. Claimants cannot rely on the accident-law aphorism that doubts are resolved in favor of the employee to meet causation in disease claims. The claimant must show, by medical probability, that workplace exposure was more likely than non-work exposure. This is particularly consequential for ubiquitous pathogens (e.g., COVID-19) and other environmentally prevalent hazards.
Practical evidentiary demands in infectious disease claims. Weeks underscores the need for tight temporal, medical, and factual proof:
- Medical timing aligned with accepted incubation windows.
- Evidence narrowing or excluding non-work contacts during the relevant period (e.g., testimony from household and ranch contacts; logs/receipts; co-worker testing and timelines; contact-tracing; consistent cluster evidence).
- Expert opinions grounded in record-supported assumptions rather than general inferences about workplace risk.
Commission’s flexibility in weighing experts. The Court reaffirms the Commission’s authority to “piece together” aspects of competing medical opinions and to resolve conflicts in expert testimony without appellate second-guessing where substantial evidence supports the result.
Open question—Is COVID-19 an occupational disease? The Court left the doctrinal question about COVID-19’s status under I.C. §§ 72-102(21)(a) and 72-438 unresolved. Future litigants will need to develop records on whether specific workplaces present hazards “peculiar to” the employment, not “common to the public in general.”
Policy implications. For employers, Weeks suggests that generalized community spread and evidence of non-work contacts will complicate compensability for infectious disease claims. For claimants in high-risk environments, success may turn on concrete, case-specific proof of workplace clusters or documented exposures and careful medical timing evidence.

Complex Concepts Simplified

Preponderance of the evidence / reasonable medical probability: The fact to be proven (here, that a work exposure caused the disease) is more likely than not true. It is not enough to show the workplace could have been a source; the workplace must be the more probable source when compared against other plausible sources.
“Actually incurred” (I.C. § 72-439(1)): Means the disease arose out of and in the course of the employment (I.C. § 72-102(21)(b) (2021)). “Arising out of” focuses on origin/causation; “in the course of” focuses on time, place, and circumstances of exposure.
Accident vs. occupational disease: An accident is a discrete event; occupational disease may develop over time from exposures that may be difficult to pinpoint. Hence, the “resolve doubts” presumption used for accidents does not carry over to proving disease causation.
Substantial and competent evidence: Evidence that a reasonable mind could accept as adequate to support a conclusion. Appellate courts do not reweigh it.
Incubation and timing in infectious disease: Medical experts assess likely exposure windows based on symptom onset and established incubation periods. In Weeks, the Commission credited testimony that symptom onset the day after exposure was not medically plausible, narrowing likely exposure dates.
Personal comfort and going-and-coming doctrines: Doctrines that sometimes treat incidental activities (e.g., restroom, refreshments) or travel as within “course of employment.” Even if an activity is in course, the claimant still must prove the disease was more likely than not acquired during that activity.

Conclusion

Weeks v. Oneida County provides a clear, consequential statement of Idaho law: the “resolve doubts in favor of the employee” concept from accident cases does not apply to occupational disease causation. In disease claims, including those involving infectious pathogens like COVID-19, the claimant must prove by a preponderance of the evidence—grounded in medical probability and record-supported assumptions—that the workplace exposure was more likely than not the source of the disease.

The Court affirmed the Commission’s decision because substantial and competent evidence supported the conclusion that alternative, non-work exposures could not be ruled out as at least equally likely sources of infection. The Commission permissibly credited expert testimony on incubation timing, rejected medically implausible exposure dates, and found the claimant’s expert’s foundational assumptions inconsistent with the record.

Notably, the Court left open whether COVID-19 qualifies as an occupational disease under Idaho’s statutory scheme. For future cases, Weeks signals that success will depend on rigorous, case-specific proof tying disease acquisition to the workplace and excluding alternative sources to a medically probable degree.