Risk factors associated with group A Streptococcus acquisition in a large, urban homeless shelter outbreak

Group A Streptococcus (GAS) is a frequent cause of outbreaks in healthcare institutions, yet outbreak reports in the literature from homeless shelters are less common, despite an increased risk of severe GAS infection in homeless populations. In 2016, we conducted a case-control study to identify significant risk factors associated with GAS acquisition in a protracted, 19-month outbreak of GAS in a large, urban men's homeless shelter in Ontario, Canada.

Cases (individuals with either clinical GAS emm74 infection or asymptomatic carriers of GAS emm74) and controls were identified from shelter residents from February to September 2016. Information on demographics, clinical presentation, pre-existing health conditions, and risk factors for GAS transmission were collected for all study participants from a variety of sources, including the public health notifiable disease information system, electronic health records, the shelter electronic information system, and interviews with client services workers.

From the multivariable logistic regression model, younger individuals (OR 9.1; 95% CI 1.57-52.9), those with previous skin conditions (OR 56.2; 95% CI 2.73-1160), and those with recent wounds (with wound care: OR 51.5, 95% CI 8.86-299, and without wound care: OR 77.4, 95% CI 7.38-812) were found to be at increased risk of acquiring GAS in this outbreak.

The outbreak investigation clearly demonstrated the need for improved wound care and infection prevention and control practices, for early screening and detection of skin and soft tissue infections, and for a comprehensive, integrated electronic information system in homeless shelters.