Q fever, a zoonotic disease caused by Coxiella burnetii, remains underrecognized and poorly characterized in terms of epidemiology. This pathogen incubates in various animal hosts, including livestock, wildlife, pets, and arthropods such as ticks. Individuals’ homelessness is at increased risk as they are consistently exposed to frequent interactions with animals such as pigeons, rodents, mosquitoes, bodies of lice, and stray dogs and cats, all potential reservoirs of C. burnetii. Ruminants are known to be a source of shedding the bacterium during birth as well, but studies have also suggested that dogs may also shed C. burnetii during reproductive disturbances, with one outbreak being when an infected dog gave birth.
Poor living conditions among individuals experiencing homelessness, including malnutrition, substance abuse, and chronic stress, can result in immunosuppression and increase susceptibility to infections, as reported in other vulnerable populations. The co-occurrence of Q fever and HIV is particularly troubling because a proportionately higher percentage of people experiencing homelessness are infected with HIV due to risk-taking behavior, including unprotected sexual activity and injection drug use, which is sometimes compounded by concurrent syphilis and hepatitis co-infection, in addition to poor access to risk reduction and treatment services. Q fever has previously been associated with social vulnerability. However, this study is the first one to exclude, as a priority, the question of whether to assess the presence of Q fever among people experiencing homelessness.
A cross-sectional study was carried out in São Paulo, Brazil, involving 203 participants experiencing homelessness. Ethical approval was granted by the national committees. Participants were recruited from a city-funded shelter for participants experiencing homelessness and participated voluntarily. Blood samples were drawn for a four-day survey in August 2020 and tested for Coxiella burnetii IgG prevalence using an indirect immunofluorescence assay. Epidemiologic data from the study population were obtained using interviews to gather all demographic information, health conditions, and risk factors such as symptoms of Q fever and HIV.
The study assessed the prevalence of antibodies against the bacterium Coxiella burnetii, which is responsible for Q fever, and HIV infection in 203 homeless individuals in São Paulo, Brazil. The results show a notable prevalence of infection. In total, 14.8% (30 individuals) were IgG antibody positive to C. burnetii with titres ranging from 64 to 1024. The results also showed that 6.4% (13 individuals) were HIV positive. There was only one individual who was both HIV positive and C. burnetii positive. There were no statistically significant associations found between C. burnetii seropositivity and any of the risk factors assessed: HIV positive, age, having pets, using drugs, eating raw meat, and domestic rats in the sleeping area.
This finding suggests the risk of C. burnetii exposure in this community may not be an issue of individual actions but environmental or infrastructural conditions. In comparison with C. burnetii studies established in Brazil, which show the prevalence of C. burnetii in the general population that normally ranges between 0.9%-8%, the prevalence of 14.8% in the homeless population is significant. Similarly elevated rates of C. burnetii have been reported in other socially underprivileged communities, such as quilombola communities (22%) and the incarcerated female population (34%), which suggests similar mechanisms of exposure to the environmentally hazardous risk factors and social deprivation.
References: de França DA, Kmetiuk LB, do Couto AC, et al. Coxiella burnetii and HIV infection in people experiencing homelessness. Sci Rep. 2025;15:28312. doi:10.1038/s41598-025-09422-z
