Since May 2022 over 20.000 monkeypox (mpox) cases have been reported from 29 EU/EEA countries, predominantly among men who have sex with men (MSM). With over 1200 cases and a crude notification rate of 70.7 per million population, the Netherlands was in the top 5 European countries most affected. The first national case was reported from May 10th, yet potential prior transmission remains unknown. We therefor performed a retrospective study to elucidate whether undetected transmission of human monkeypox virus (hMPXV) occurred prior to the first reported cases in the two largest cities in the Netherlands, Amsterdam and Rotterdam.
Methods
Data from the two largest Centers for Sexual Health in the Netherlands were used. We retrospectively tested stored samples for hMPXV using an in-house developed and validated qPCR. Stored samples comprised anorectal samples that were positive for Chlamydia or Gonorrhoea (Ct/Ng) and all collected ulcer samples. Whole genome sequencing was performed for hMPXV positive samples. For phylogenetic analysis we used all available Genbank sequences and added the Dutch strains generated as part of this study.
Results
We tested 262 (169 in Amsterdam; 93 in Rotterdam) anorectal samples that were positive for Ct/Ng and 137 ulcer samples (125 Amsterdam, 12 Rotterdam) collected between February 14 and May 18, 2022 on the presence of hMPXV. Two hMPXV positive samples were identified, one from an anorectal sample and one from an ulcer sample, both collected in the first week of May (week 18), 2022. Both samples were from MSM, one had symptoms of proctitis and one had multiple ulcers. The anorectal hMPXV positive sample was successfully sequenced. This sequence, like all other Dutch sequences belonged to the clade IIb cluster (B.1) with a close relation to international strains of hMPXV (figure).
Conclusion
The first mpox cases in the Netherlands coincided with the first cases reported in the United Kingdom, Spain and Portugal. We found no evidence of widespread hMPXV transmission in Dutch sexual networks of MSM prior to May 2022. Likely, the hMPXV outbreak expanded across Europe within a short period in the spring of 2022 in an international highly intertwined network of sexually active MSM.
