In their Correspondence, Abdullah Reda and colleagues emphasised the importance of undiagnosed mpox (formally known as monkeypox) cases and called for surveillance with rapid diagnostic or home-based tests.1 We agree that the threshold for testing or screening at-risk populations should be low at the beginning of an epidemic with a new pathogen, to ascertain the nature and prevalence of atypical presentations.
Since we discovered three asymptomatic mpox cases by retrospectively testing stored samples taken for chlamydia and gonorrhoea testing in May, 2022,2 we were interested to assess whether in the following months, more cases occurred among men who have sex with men (MSM) who did not fulfil the WHO case definition of a suspected mpox case. We decided to expand the retrospective testing programme to samples collected in June, 2022, and to offer mpox testing to HIV-positive MSM and HIV-negative MSM using HIV pre-exposure prophylaxis, who attended our sexual health clinic for anorectal chlamydia or gonorrhoea testing or screening from July to September, 2022. Our analysis detected seven previously undiagnosed mpox cases among the samples from 146 MSM in June, and seven additional cases among 181 prospectively screened MSM between July and September (table ). Among these 14 mpox cases, five (35·7%) were HIV-positive, the remaining cases used HIV pre-exposure prophylaxis. The median age of participants was 41 years (IQR 38·0–43·0). All mpox cases were from before Aug 25, 2022, and only two fulfilled the WHO definitions of a suspected mpox case or European Centre for Disease Prevention and Control (ECDC) defined probable mpox case that were in effect at the time. These two people with mpox had subtle macular skin lesions and lymphadenopathy. The WHO and ECDC updated their mpox case definitions on Aug 25, and Sept 3, 2022, respectively, to include cases without skin lesions but with lymphadenopathy, mucosal lesions (including proctitis), or prodromal symptoms after contact with aanother person with mpox. Among our 12 remaining people with mpox, eight fulfilled these updated case definitions at the time of sampling due to proctitis (n=6) or lymphadenopathy (n=2), and three did so within the next 7 days because they developed typical febrile mpox skin lesions (n=2) or proctitis (n=1). One man did not meet any mpox case definitions as he only had prodromal symptoms without exposure to another person with mpox.
Table.
Mpox patient characteristics and outcomes
|
Diagnosis |
Overall (n=14) | |||
|---|---|---|---|---|
| Retrospective (n=7) | Prospective (n=7) | |||
| Age, median (IQR) | 41 (39·0–42·0) | 40 (38·0–47·5) | 41 (38·0–43·0) | |
| Sexual behaviour | ||||
| Male-to-male sexual intercourse | 7 (100%) | 7 (100%) | 14 (100%) | |
| Multiple or anonymous sex partners in the previous 21 days | 7 (100%) | 6 (85·7%) | 13 (92·9 %) | |
| HIV status | ||||
| Positive | 4 (57·1%) | 1 (14·3%) | 5 (35·7%) | |
| Negative and on PrEP | 3 (42·9 %) | 6 (85·7 %) | 9 (64·3 %) | |
| Coinfection | ||||
| Gonorrhoea | 3 (42·9%) | 1 (14·3%) | 4 (28·6%) | |
| Chlamydia | 1 (14·3%) | 1 (14·3%) | 2 (14·3%) | |
| Mpox symptoms | ||||
| Subtle skin lesions and lymphadenopathy | 2 (28·6%) | 0 | 2 (14·3%) | |
| Proctitis with or without fever | 4 (57·1%) | 3 (42·9%)* | 7 (50%)* | |
| Lymphadenopathy | 1 (14·3%) | 1 (14·3%) | 2 (14·3%) | |
| Typical monkeypox skin lesions with fever | 0 | 2 (28·6%)† | 2 (14·3%)† | |
| Prodromal symptoms only | 0 | 1 (14·3%) | 1 (7·1%) | |
| Case definition | ||||
| WHO suspected case (May 21, 2022) | 2 (28·6%) | 2 (28·6%)† | 4 (28·6%)† | |
| ECDC probable case (before Sept 8, 2022) | 2 (28·6%) | 2 (28·6%)† | 4 (28·6%)† | |
| WHO (Aug 25, 2022) and ECDC (Sept 3, 2022) revised definition of suspected case | 7 (100%) | 6 (85·7%)‡ | 13 (92·9%)‡ | |
| Sample type | ||||
| Anorectal swab | 3 (42·9%) | 4 (57·1%) | 7 (50%) | |
| Pooled sample§ | 4 (57·1%) | 3 (42·9%) | 7 (50%) | |
| Monkeypox virus-PCR, ct value (IQR) | 21 (20·0–23·4) | 28 (25·5–30·3) | 28 (21·5–27·5) | |
Data is n/N (%). ct=cycle threshold. ECDC=European Centre for Disease Prevention and Control. PrEP=HIV pre-exposure prophylaxis.
Anorectal swab, oropharyngeal swab, and urine sample.
One man was presymptomatic at the time of sampling.
Two men were presymptomatic at the time of sampling.
Three men were presymptomatic at the time of sampling.
Screening for mpox among individuals at high-risk, diagnosed 12 cases that did not fulfil the preliminary mpox case definition, of whom three individuals were presymptomatic and one individual only had prodromal symptoms. Our findings underscore the accuracy of the updated mpox case definition and suggest that the prevalence of asymptomatic mpox cases should not be overestimated, as we found no asymptomatic mpox cases.
Acknowledgments
This research was approved by the Institutional Review Board of the Institute of Tropical Medicine Antwerp, Antwerp, Belgium, on Sept 30, 2022, (ref 1629/22) and the Ethical Committee of the University Hospital Antwerp, Antwerp, Belgium, on Oct 17, 2022 (ref 3863). All authors declare no competing interests. CVD, IDB, KV, and MVE contributed equally.
Contributor Information
ITM Monkeypox Study Group:
Christophe Van Dijck, Irith De Baetselier, Chris Kenyon, Isabel Brosius, Laurens Liesenborghs, Dorien Van den Bossche, Eric Florence, Johan van Griensven, Emmanuel Bottieau, Patrick Soentjens, Nicole Berens-Riha, Thibaut Vanbaelen, Maartje Van Frankenhuijsen, Marc Vandenbruaene, Veerle Huyst, Kristien Wouters, Ludwig Apers, Ilse Kint, Séverine Caluwaerts, Jasmine Coppens, Marjan Van Esbroeck, and Koen Vercauteren
References
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