Investigation and response to an outbreak of mpox cases linked to a high-risk group event in Southeast Queensland in May 2024
DOI:
https://doi.org/10.33321/cdi.2026.50.004Keywords:
infectious diseases, public health, sexually transmitted infections, emerging infectious diseases, applied epidemiology, virologyAbstract
Objective
The primary aim of this paper is to describe the outbreak investigation and public health response to a cluster of mpox cases that occurred in Southeast Queensland; and to investigate transmission dynamics to inform contact management.
Background
The transmission of mpox in Australia has continued to circulate among the men who have sex with men community, since the declaration of the global outbreak of clade IIb in 2022. In May 2024, an outbreak investigation was carried out following the admission of an mpox case to a Queensland hospital, which precipitated a response coordinated by two metropolitan public health units (Metro North and Metro South) in Brisbane.
Methods
A prospective cohort study was conducted to follow up attendees of an intimate group event over a 21-day period. From 21 event attendees, 16 were able to be contacted by public health clinicians, and were included in the cohort. Case histories and their respective contacts were identified and classified as high, medium or low risk. Descriptive statistics were conducted, and relative risk was determined for developing infection after attendance at the group event, when accounting for the level of vaccination against mpox. Whole genome sequencing was performed on collected pathology specimens, and phylogenetic analysis was conducted to support epidemiological investigations.
Findings
A total of ten cases of mpox were detected, among a cohort of 16 males with differing levels of vaccination. Transmission of mpox occurred exclusively among high-risk contacts; no transmission was observed to medium- or low-risk contacts. Laboratory investigations revealed that all cases were of human MPXV clade IIb. Complete vaccination was a protective factor against development of mpox (relative risk = 0.33; 95% confidence interval: 0.06–1.88), compared with partial or no vaccination, after attendance at the high-risk exposure event.
This outbreak resulted in 34 contacts, of which one high-risk contact became a secondary case. Findings from this investigation suggest there is less urgency for follow-up of household contacts and other medium- and low-risk contacts of mpox, compared with high-risk contacts. Fostering a rapport during telephone interviews with cases and contacts was found to be crucial to the overall attainment of accurate case histories, highlighting the need for the development of trust when interacting with members of priority groups. This outbreak investigation describes a comprehensive public health response attributed to the coordination of a range of public health workers in the Southeast Queensland area.
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