Which of the following circumstances must be reported promptly to USDA?

The most appropriate circumstance that must be reported promptly to the USDA is serious deviation from the Guide (unless previously approved). This type of deviation poses significant concerns regarding animal welfare, compliance with regulations, and the integrity of research. The USDA requires that any such serious deviations are reported to ensure that appropriate oversight and corrective actions are taken.

Reporting requirements are mandated under the Animal Welfare Act, which emphasizes the importance of adherence to established guidelines for humane care and use of laboratory animals. Thus, it is critical to communicate any serious deviations promptly to maintain compliance with federal regulations and uphold animal welfare standards.

While suspension of an activity by the IACUC and serious continuing noncompliance with PHS policy are certainly serious issues, they are generally reported to other authorities or require different management processes depending on institutional policies and specific circumstances. Hence, not all situations listed carry the same reporting requirement to USDA, making "none of the above" the incorrect choice.