Another Perfect Storm: Shigella Men Who Have Sex with Men, and HIV

Extract

Shigella species are a significant cause of bacterial dysentery worldwide, with ∼165 million cases every year, leading to 1 million deaths annually [1]. Nearly 450,000 Shigella infections, causing significant morbidity, are reported each year in the United States [2]. Many of these cases occur in children or in health care institutions or are imported through travel abroad. In the mid-1970s, outbreaks of Shigella infection among adults in New York and San Francisco raised the possibility that Shigella species may be sexually transmitted, with most infections occurring in men who have sex with men (MSM) [3, 4]. Since these early observations, Shigella infection appears to be more frequent among MSM than among other adult populations, via direct fecal-oral transmission either through accidental inoculation of contaminated stool or through direct oral-anal contact [5,6,7,8–9].

The efficiency of this sexual transmission is likely fueled by several elements, both biological and behavioral in nature (figure 1). A very small inoculum of Shigella—as low as 10 organisms—is able to cause disease [10]. Even the accidental ingestion of minute amounts of fecal material during sexual activity could deliver a sufficient inoculum. Often transmitted through ingestion of contaminated food or water, Shigella species survive the chemical barriers of the stomach and thrive in the colon, leading to tissue invasion and disease [11]. Biological factors in the host likely also participate in the apparent frequency of Shigella infection among MSM; the immunodeficiencies related to the high prevalence of HIV infection among these men may drive transmission [8, 12]. Social adaptation by MSM in the age of HAART may affect behaviors that influence transmission of enteric pathogens, and travel-related infections may introduce Shigella species to networks of susceptible persons.