Shigellosis Outbreak Among Los Angeles MSM Follows Similar Outbreak in 2015

An outbreak of Shigellosis, a common diarrheal disease caused by a group of bacteria called Shigella, is affecting men who have sex with men in Los Angeles, Pasadena, and Long Beach. MSM are more likely to acquire shigellosis, and people with HIV can have more severe and prolonged shigellosis, including having the infection spread into the blood, which can be life-threatening.

The Los Angeles County HIV Drug & Alcohol Task Force reported that on August 8, the California Department of Public Health (CDPH) found a cluster of nine Shigella flexneri cases, with an uncommon strain, serotype 7 (also known as 1c or provisional 88-893), from LAC, Pasadena, Long Beach and nearby counties. Three were known to require hospitalization and one patient, an LAC resident, died. All patients were men, aged between 28 and 57 years old.

Four self-identified as gay or bisexual and four were immunocompromised. Common symptoms include fever, diarrhea, and abdominal pain; four of six patients for whom data were available indicated that the diarrhea was bloody. No patients provided a history of recent domestic or international travel.�Three strains tested for antimicrobial susceptibility showed resistance to ampicillin and trimethoprim/sulfamethoxazole (Bactrim, Septra). �

Since August 19, an additional four cases were reported with infection caused by the same S. flexneri serotype; further demographic and clinical data are pending.�No other S. flexneri, serotype 7 isolate has been identified from LAC since 2014.

A total of 49 and 48 cases of S. flexneri were reported to LAC DPH through August 2015 and 2016, respectively. Eighty-eight percent of the cases in both years were men. Shigella is most often spread person-to-person or by eating food contaminated by someone who is infected. Transmission is fecal-oral; MSM are known to be at increased risk.

This follows a similar situation in July 2015, when the CDC reported that Shigella sonnei infections with a specific pulsed-field gel electrophoresis (PFGE) pattern linked to a multistate outbreak were recognized among MSM in the Portland metropolitan area, and an outbreak investigation was initiated.

During November 2015, isolates with PFGE patterns indistinguishable from the outbreak strain were identified in cases reported in four women, none of whom had epidemiologic links to other affected persons; however, three reported homelessness. In the ensuing months, additional S. sonnei infections were reported among homeless persons in the Portland area.

Shigella is the third most common cause of bacterial gastroenteritis in the United States, resulting in approximately 500,000 infections, 100,000 hospitalizations, and 500 deaths annually. Shigella is transmitted by the fecal-oral route and is highly infectious, highlighting the importance of hygiene in outbreak control. In high-income countries, children, travelers to low-income countries, and MSM are groups at increased risk for infection; in low-income countries, groups with inadequate access to hygiene and sanitation are at increased risk.

During July 1, 2015-June 30, 2016, a total of 103 Shigella infections with indistinguishable PFGE patterns were reported in Oregon. All cases occurred in adults aged 18 years; 77 (75 percent) were men, 38 (49 percent) of whom self-identified as MSM. Homelessness was self-reported by three (8 percent) MSM and 41 (63 percent) of 65 persons who did not self-identify as MSM. Twelve (12 percent) persons, including two MSM, reported connections to homeless persons (e.g., volunteer work) during their incubation period.

During July-October, 2015, 18 (82 percent) Shigella cases occurred in MSM, compared with 20 (25 percent) during November 2015-June, 2016 (prevalence ratio [PR]�=�3.3; 95 percent confidence interval [CI]�=�2.2-5.1); Before November 2015, only three (14 percent) Shigella patients were homeless, including one who self-identified as MSM. After November 1, 2015, 41 (51 percent) were homeless (PR�=�3.7; 95 percent CI�=�1.3-10.9).

The focus of outreach efforts expanded from prevention of sexual transmission among MSM to addressing access to hygiene and sanitation among homeless persons, including distribution of hand sanitizing wipes, site visits to shelters and encampments, and alerts to safety-net providers.

As the outbreak progressed, the percentage of Shigella infections among MSM declined, while infections among homeless persons increased. Continuing infections among MSM with no connection to the homeless community indicate ongoing transmission in both populations. In retrospect, reports of illnesses among women were the first indication of Shigella infections in homeless persons. Early detection of new populations at risk is important because outbreak investigation and control measures might require revision. Adding questions about sexual practices and housing status to routine Shigella questionnaires might help identify outbreaks in these groups.