By Stan Deresinski, MD, FACP, FIDSA
Clinical Professor of Medicine, Stanford University
SYNOPSIS: The prevalence of Shigella resistant to azithromycin, ciprofloxacin, ceftriaxone, trimethoprim-sulfamethoxazole, and ampicillin is increasing.
SOURCE: California Department of Public Health. Health Advisory. Rise in extensively drug-resistant Shigella strains—January to May 2024. Aug. 9, 2024. https://www.cdph.ca.gov/Programs/OPA/Pages/CAHAN/Rise-in-Extensively-Drug-Resistant-Shigella-Strains.aspx
The California Department of Public Health (CDPH) posted a Health Advisory on Aug. 8, 2024, alerting healthcare providers to a significant increase in the number of cases of extensively drug-resistant (XDR) Shigella infections so far in 2024. The Centers for Disease Control and Prevention (CDC) defines XDR Shigella as strains that are resistant to all commonly recommended empiric and alternative antibiotics: azithromycin, ciprofloxacin, ceftriaxone, trimethoprim-sulfamethoxazole (TMP-SMX), and ampicillin. In this report, isolates were determined to be XDR by whole genome sequencing (WGS).
First detected in California in 2017, the prevalence of XDR infections increased to 2.2% of Shigella isolates in 2022, with a further increase to 6.8% in 2023. During the first five months of 2024, however, 118/978 (12%) were XDR, with 37% recovered in Southern California and 44% in the San Francisco Bay area. Of the total, 78% were identified as Shigella sonnei and 22% as Shigella flexneri.
While shigellosis historically was largely a childhood disease, the median age of patients with XDR Shigella infection in California in 2014 was 38 years and one-half were 25-44 years of age. Furthermore, 102 (86%) were adult males. Among the 64 for whom the information was available, 48 (75%) self-identified as men who have sex with men (MSM). Among the 94 with available information, eight (9%) were experiencing homelessness while 9/88 reported international travel.
COMMENTARY
The CDC has reported that in the United States, approximately 5% of Shigella strains were XDR in 2022, while in 2015 no XDR strains were identified.1 The overall U.S. data were similar to those reported in California for 2024. Thus, 66% and 34% were S. sonnei and S. flexneri. The median patient age was 42 years, 82% were men, and, among those for whom the information was available, 88% were MSM. Similar demographics have been seen in other countries, such as the United Kingdom.2 Thus, it is apparent that XDR Shigella infections are on the rise and appear to be driven largely by MSM, while homelessness and, in the United States, international travel were additional risk factors.
Shigellosis generally is self-limited, and antibiotic treatment, although it may shorten the duration of illness by approximately two days, often is not necessary. The CDC states that treatment may, however, reduce the likelihood of transmission to immunocompromised patients.1 If a culture-independent test, such as multiplex polymerase chain reaction (PCR), is used to identify Shigella, the clinician should ascertain that the clinical laboratory automatically cultures the sample and performs antibiotic susceptibility testing on relevant isolates. Cases should be reported immediately to the local health department.
Antibiotic treatment of XDR Shigella infections remains problematic. Among drugs that have been suggested are carbapenems, advanced generation tetracyclines, fosfomycin, and pivmecillinam (recently U.S. Food and Drug Administration approved for treatment of uncomplicated urinary tract infections). However, relevant published clinical data are almost nonexistent.
REFERENCES
- Centers for Disease Control and Prevention. Health Advisory. Increase in extensively drug-resistant shigellosis in the United States. Feb. 24, 2023. https://emergency.cdc.gov/han/2023/han00486.asp
- Thorley K, Charles H, Greig DR, et al. Emergence of extensively drug-resistant and multidrug-resistant Shigella flexneri serotype 2a associated with sexual transmission among gay, bisexual, and other men who have sex with men, in England: A descriptive epidemiological study. Lancet Infect Dis 2023;23:732-739.
