Severe Shigella Infections Increasing in Homeless Patients

Cases of multidrug-resistant Shigella sonnei infections among patients experiencing homelessness in Vancouver have increased sharply, according to infectious disease experts.

Between 2015 and 2022, the rate of S sonnei infections rose from 8.3 cases per year to 56.5 cases per year. At the beginning of the study period, the population primarily affected with shigellosis was men who have sex with men. The most affected population is now patients experiencing homelessness.

Not only are cases increasing but also the disease itself has become more severe. Many cases resist all first- and second-line antibiotics, sometimes resulting in hospitalization, bacteremia, or death.

The findings were published on November 21 in Clinical Infectious Diseases. 

Severe Diarrheal Illness

“We were noticing an increasing number of patients with severe diarrheal illness, and it turned out that many of them were infected with Shigella, something we tended to see only in men who have sex with men,” senior author Marc Romney, MD, clinical professor of pathology and laboratory medicine at the University of British Columbia in Vancouver, told Medscape Medical News.

“What struck us was not only the increase in cases but also that there were females as well. And a lot of these people were homeless. We were also struck by the severity of the infections we were seeing. Some of these patients had not just diarrhea but also severe, bloody diarrhea that required hospitalization. They would be seen by a gastroenterologist and be diagnosed with infectious colitis due to Shigella,” Romney said.

Also concerning was the fact that the strain causing most of the infections was multidrug-resistant. “There were no first- or second-line antibiotics we could use. Some of our patients didn’t want to stay in hospital, and we were looking for an oral antibiotic, but there were none. We had to give ceftriaxone via IV infusion, so this became a complicated treatment issue, on top of the multidrug resistance issue,” he said.

Between 2015 and 2022, Romney and his team analyzed 163 patients with S sonnei infections in Vancouver. Data collected from 2015 to 2020 were designated as historical, and data collected from 2021 to 2022 were designated as recent. The researchers used whole genome sequencing to identify S sonnei genotype and predict antimicrobial resistance.

Of these 163 cases, 50 were detected in the historical period, and 113 in the recent period. Over time, the primary population characteristics associated with Shigella infection shifted from men who have sex with men (n = 45 cases, 98%) to patients experiencing homelessness (n = 86 cases, 77%).

The rate of severe shigellosis was significantly higher in the recent period (n = 69, 61%) compared with the historical period (n = 7 cases, 14%, P S sonnei, 3.6.1.1.2, resisted all first-and second-line agents.

Shigella is very infectious, and a small amount will cause severe infection, Romney noted. It is transmitted by the fecal-oral route. 

“Bad sanitation and hygiene and overcrowding are huge contributing factors for shigellosis. People experiencing homelessness have a lot of difficulty washing their hands, and if food is provided to them and they are unable to wash their hands, they can be contaminating their food. There can also be fecal matter contaminants on surfaces in homeless shelters. What makes Shigella unique is that its infectious dose is very low. It’s highly infectious: Much more infectious than most other bacteria that cause infections in humans,” he said.

‘A Concerning Rise’

“While the sample size is limited, the study does document a concerning rise in multidrug resistant S sonnei in people experiencing homelessness, a population with high rates of substance use disorder, as well as psychiatric illness. This population is often challenged by malnutrition and various other health issues,” Stephen Hoption Cann, PhD, professor of population and public health at the University of British Columbia, told Medscape Medical News. 

Hoption Cann did not participate in the current study. “This is likely an underlying factor for the high severity of disease seen in this population,” he said. 

“This report suggests that the infection, which was most seen in men who have sex with men, has likely spread to those experiencing homelessness. For the former population, the disease is primarily spread through sexual transmission, while in the latter group, it’s spread environmentally through fecal contamination of surfaces and lack of hand washing,” said Hoption Cann.

“So, what can be done? There is no vaccine for Shigella, although some are under study. While improved hygiene practices would reduce transmission, this is unlikely to occur in this setting of homelessness. The most successful intervention would likely be getting people who are experiencing homelessness access to treatment for substance use disorder and psychiatric illness. The province of British Columbia has stated that they are trying to increase treatment availability, so one can hope this will lead to improvements down the road.”

Hoption Cann cautioned that the authors’ suggestions of reducing shigellosis in this population by improving sanitation, access to handwashing and hygiene facilities, and nutrition would likely be ineffective in the homeless population.

“There is access to food banks and nonprofits that offer reasonably healthy meals, but without treatment for substance use disorder and psychiatric illness, this population would not consistently take advantage of these options,” he said. 

The study was conducted without external funding. Romney and Hoption Cann declared having no relevant financial relationships.