Shifting dominance of Shigella species in men who have sex with men

Historically, Shigella sonnei has dominated other Shigella species infection in men who have sex with men (MSM) in Montréal. In early 2010, Toronto reported increased proportions of the more pathogenic S. flexneri, HIV co-infection and MSM in shigellosis cases since 2009. Analytical methods were used to assess whether S. flexneri had dominated Montréal's MSM cases since 2009 and whether changes had occurred in notifications in MSM and HIV-co-infected MSM. S. flexneri increased by 6·7% per month since 2007 and predominated in MSM since 2009 without changes in HIV co-infection or similar shifts in the general population. The results suggest that the surveillance of Shigella species in order to detect species shifts is beneficial for surveillance, given the potential for increased transmission and severity of S. flexneri in HIV-positive MSM.