How feasible and accurate are self-collected specimens for the diagnosis of monkeypox?

In a recent study published on medRxiv* server, a team of researchers evaluated the performance of self-collected clinical specimens from patients infected with monkeypox virus (MPXV) compared to physician-collected clinical specimens, including skin lesions, pharyngeal and rectal swabs in diagnostic tests.

Study: To assess the accuracy of self-collected swabs for the diagnosis of monkeypox. Image Credit: Corona Borealis Studio/Shutterstock

Background

Self-sampling has proven to be a reliable strategy for diagnosing sexually transmitted diseases (STDs), such as chlamydia and gonorrhea, based on nucleic acid amplification testing and recently coronavirus disease 2019 (COVID-19). However, this approach has not yet been tested and validated for the diagnosis of Monkeypox.

About the study

In the present study, researchers performed an evaluation of the diagnostic accuracy of self-sampling in MPXV parameters. They recruited people from three centers in Spain who had lesions indicative of MPXV infection within ten days of screening for the study. A dermatologist or STD specialist clinically evaluated these patients and enrolled those suspected of having MPXV infection into the study.

All study participants received a home testing kit with instructions, including dacron-tipped swabs for sample collection, pre-labeled swab containers, and a mailing envelope. The team trained these individuals in self-collection of samples and instructed them to self-collect swabs from skin lesions, oropharynx, and rectum on day 1 of the study.

The participants stored the self-collected samples at 4°C after collection and contacted the courier service, which transferred these samples to a microbiology laboratory in Spain for diagnostic testing.

The researchers analyzed swabs using quantitative polymerase chain reaction (qPCR), and all patients with positive samples taken by a physician on day 0 were included in the study analyses. All of these participants had confirmed MPXV infection.

Study results

In total, the study recruited 50 patients with suspected MPXV infection. All patients were male, with a mean age of 33.5 years. They had qPCR-confirmed MPXV infection in at least one of the self-collected diagnostic samples. At baseline, the number of skin lesions and pharyngeal and rectal swabs were 49, 38, and 11, respectively. All self-collected skin lesion swabs were positive for MPXV DNA. However, only 68% and 82% of oropharyngeal and rectal swabs were positive for MPXV DNA.

The researchers noted the highest overall agreement of 98% in skin lesion swabs. Surprisingly, only one individual tested negative in the doctor-collected skin lesion swab and positive in the self-collected skin lesion swab sample. Similarly, the overall agreement for the throat and rectal samples was 79% and 90%, with kappa values ​​of 0.49 and 0.6, respectively.

Additionally, the researchers noted no significant difference in cycle threshold (CJ) values ​​between physician-collected and self-collected skin lesion and throat samples. Conversely, self-collected rectal swabs had a higher CJ values ​​than samples collected by physicians, with an absolute difference of 5.5; and a 95% confidence interval (CI). Middle CJ values ​​for physician-collected and self-collected swabs were 22.5 and 23.2, respectively, with an absolute difference of 0.7; and a 95% CI.

conclusion

According to the authors, this is the first study to demonstrate the feasibility of the self-sampling approach for the diagnosis of MPXV. Overall, self-collected swabs had high accuracy and comparable viral loads to swabs collected by physicians. Skin swabs taken by patients are generally not used to diagnose common skin diseases with blisters, such as herpes or chicken pox. However, these patient-collected swabs from skin lesions had high performance characteristics comparable to physician-collected swabs.

Overall agreement between physician-collected and self-collected oropharyngeal swabs was lower than for other specimens, likely due to variation in specimen quality. However, fluctuations in viral load in the pharynx are also possible.

In summary, the self-sampling approach explored in the present study offered many significant benefits for patients and disease control. It facilitated the integration of monkeypox into routine testing with other STDs in high-risk populations. Future studies should optimize sample collection and include more samples, such as saliva, to accentuate the ease of diagnostic testing.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered conclusive, guide clinical practice/health-related behaviors, or treated as established information.

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