Abstract and Introduction

Abstract

Annually, Shigella spp. cause ≈188 million cases of diarrheal disease globally, including 500,000 cases in the United States; rates of antimicrobial resistance are increasing. To determine antimicrobial resistance and risk factors in San Diego, California, USA, we retrospectively reviewed cases of diarrheal disease caused by Shigella flexneri and S. sonnei diagnosed during 2017–2020. Of 128 evaluable cases, S. flexneri was slightly more common than S. sonnei; most cases were in persons who were gay or bisexual cisgender men, were living with HIV, were unhoused, or used methamphetamines. Overall, rates of resistance to azithromycin, fluoroquinolones, ampicillin, and trimethoprim/sulfamethoxazole (TMP/SMX) were comparable to the most recent national data reported from the Centers for Disease Control and Prevention; 55% of isolates were resistant to azithromycin, 23% to fluoroquinolones, 70% to ampicillin, and 83% to TMP/SMX. The rates that we found for TMP/SMX were slightly higher than those in national data.

Introduction

Shigella bacteria are facultatively anaerobic, nonmotile, gram-negative bacilli and a common global cause of infectious diarrhea, especially in low-income settings^[1]. They are relatively resistant to the high acidity of the stomach and can survive transit into the small intestine, where they multiply and pass into the colon, invading colonic cells and causing diarrhea. As few as 10–100 organisms are capable of causing disease^[2]. This low infectious dose increases transmission by the fecal–oral route or via contaminated food and water. Globally, Shigella spp. cause an estimated 188 million cases of diarrheal disease annually and account for 164,000 deaths^[1] particularly in children.

In the United States, ≈500,000 cases of shigellosis occur annually; 81% are caused by Shigella sonnei, followed by S. flexneri (12.6%), S. boydii (0.2%), and S. dysenteriae (0.1%)^[3]. Most transmission occurs via the fecal–oral route, at locations such as daycare centers, but transmission can also occur after ingesting contaminated food or drinking water, after ingesting untreated recreational water^[4], and among men who have sex with men (MSM). Among MSM, multiple outbreaks have been described in Montreal, Quebec, Canada^[5,6], and Germany^[7]; and in the United States^[8,9] including Minnesota^[10]; the Chicago, Illinois, and Minneapolis-St. Paul, Minnesota, regions^[11]; and New York, New York^[12].

For children and adults with symptomatic shigellosis, antimicrobial therapy is typically recommended because it shortens symptom duration and decreases the duration of bacterial shedding in adults^[13] and children^[14–17]. For children, antimicrobial therapy should be guided by local resistance profiles. For adults, empiric antimicrobial therapy selection should be guided by local resistance profiles as well as patient demographics. For example, in parts of Asia, widespread resistance to azithromycin, ceftriaxone, and ciprofloxacin has been reported^[18,19]. In addition, increasing antimicrobial resistance has been found in certain groups, such as MSM, and has also been associated with travel^[20] including increasing resistance to first-line agents such as fluoroquinolones^[5,7] and azithromycin^[8] Last, susceptibilities obtained from culture should be used in the event of treatment failure.

To determine antimicrobial resistance and risk factors in the San Diego, California, USA, area, we investigated cases of symptomatic shigellosis causing diarrheal disease at the University of California San Diego Health System and San Diego Veterans Affairs Medical Center over a 3-year period. The study was approved by the Human Research Protection Program at University of California San Diego Health and the San Diego Veterans Affairs Institutional Review Board.