Background Since 2011, an increase in Shigella flexneri has been observed in men due to faecal-oral transmission associated with sexual contact between men who have sex with men (MSM). Sexual history is not routinely collected for cases of gastrointestinal infections.
Aims To use gender ratio to detect greater than expected numbers of gastrointestinal infections in MSM.
Methods We examined annual male to female ratios of laboratory confirmed patient-episodes from those aged 16–65 years with no known history of travel for eight gastrointestinal pathogens (Campylobacter, Cryptosporidium, Giardia, Hepatitis A, Norovirus, Salmonella, Shigella, and VTEC) in England between 2003 and 2013. Chi-squared tests for linear trend were conducted and a male to female ratio of more than two was considered suggestive of an excess. Sub-analyses by age and high-risk areas (London, Brighton and Manchester) were conducted.
Results An increased linear trend and excess of male episodes was observed for Shigella (p < 0.001; m:f ratio of 2.0 and 2.5 in 2012 and 2013, respectively) but not the other gastrointestinal infections. Consistent with MSM-mediated transmission, the excess of male Shigella episodes was most pronounced among those aged 25–49 years (ratios of 2.4 and 2.9) and those in high-risk areas (ratios of 2.9 and 4.0); no excess was observed among children.
Conclusion This method identified the recent outbreak of Shigella and routine application might alert public health authorities to some future gastrointestinal infection outbreaks in MSM. Utility of this approach to detect excess episodes among MSM is likely to be pathogen specific and dependent on several factors including R0.
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