Top 5 Takeaways

1. Identification of False-Positive Results: The report highlights three cases of false-positive Orthopoxvirus PCR test results in individuals with atypical rashes and no epidemiologic link to monkeypox, emphasizing the need for cautious interpretation of test results.
2. High Cycle Threshold (Ct) Values: In all three cases, the initial positive tests had high Ct values (≥34), suggesting a low viral load and underscoring the importance of retesting in such scenarios.
3. Revised Testing Guidance: The CDC recommends reextraction and retesting of specimens with high Ct values (≥34) in cases without clear epidemiologic links or typical clinical presentations.
4. Importance of Epidemiologic Link: The report stresses the significance of considering epidemiologic links and risk factors in testing and diagnosis, especially in non-MSM populations and atypical presentations.
5. Broader Implications for Public Health: These findings highlight the importance of verifying positive diagnostic results and considering alternative diagnoses, particularly in low-incidence populations.

Note:

This MMWR Article was created prior to the conventional renaming of Monkeypox to its more standard and appropriate name, Mpox. To avoid confusion, Monkeypox is retained when writing this article, but all future works should use Mpox.

Original Article Author and Citation

Corresponding Author

Faisal Minhaj, fminhaj@cdc.gov

Suggested Citation

Minhaj FS, Petras JK, Brown JA, et al. Orthopoxvirus Testing Challenges for Persons in Populations at Low Risk or Without Known Epidemiologic Link to Monkeypox — United States, 2022. MMWR Morb Mortal Wkly Rep 2022;71:1155–1158. DOI: http://dx.doi.org/10.15585/mmwr.mm7136e1.

Summary

This report discusses three patients with atypical rashes and no known epidemiologic link to monkeypox who received false-positive Orthopoxvirus PCR test results. The cases demonstrate the challenges of interpreting test results in low-risk populations and emphasize the need for retesting specimens with high Ct values (≥34).

Methods

The report analyzed cases where individuals without traditional risk factors or epidemiologic links to monkeypox received initial positive test results. These results were later determined to be false positives based on high Ct values, leading to revised testing protocols and additional confirmatory testing.

Discussion

The report underscores the importance of considering epidemiologic links and symptom presentation in testing for monkeypox. The findings highlight the potential for false positives in low-risk groups, the need for cautious interpretation of high Ct values, and the role of confirmatory testing in accurate diagnosis.

Conclusion

The evaluation of these patients illustrates the need for caution in interpreting laboratory test findings for monkeypox, especially in patients with low pretest probability of infection, and the importance of confirming positive results in low-incidence populations.

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