Shigella: The New Superbug?

By Stan Deresinski, MD, FACP, FIDSA

Clinical Professor of Medicine, Stanford University

SYNOPSIS: Five percent of Shigella isolates in the United States in 2022 were extensively drug-resistant.

SOURCE: Centers for Disease Control and Prevention. Health Alert Network (HAN) – 00486. Increase in extensively drug-resistant shigellosis in the United States. Feb. 24, 2023. https://emergency.cdc.gov/han/2023/han00486.asp

The Centers for Disease Control and Prevention (CDC) has issued an alert indicating that there has been an important increased frequency of infection with extensive drug-resistant (XDR) Shigella in the United States. While none were reported as recently as 2015, in 2022 approximately 5% of isolates were XDR. The CDC defines XDR Shigella as being resistant to azithromycin, ciprofloxacin, ceftriaxone, trimethoprim-sulfamethoxazole, and ampicillin. Two-thirds of the 239 XDR isolates recovered from 2015-2022 were Shigella sonnei and one-third were Shigella flexneri.

Affected patients ranged in age from 1-83 years (mean age, 42 years). Among 232 patients for whom the information was available, 82% were adult men, 13% were adult women, and 5% were children. Many of the men reported male-male sexual contact.

COMMENTARY

High rates of Shigella resistant to various antibiotics have been reported previously in Asia, Africa, and, to a lesser extent, some other regions. In the United States, largely sporadic resistance to commonly used antibiotics has been seen, especially in returned international travelers, homeless individuals, people living with human immunodeficiency virus (HIV), and men who have sex with men (MSM).

Shigellosis usually is self-limited, but antibiotic therapy shortens the duration of symptoms by approximately two days. The CDC indicates that additional reasons for antibiotic therapy include possible reduced transmission during outbreaks, within institutions, in food handlers, in immunocompromised patients, and in individuals living with HIV.

Commonly used empiric antibiotics include a fluoroquinolone or azithromycin, but the 2018 Infectious Diseases Society of America (IDSA) guideline also suggests ampicillin, ceftriaxone, or trimethoprim-sulfamethoxazole as alternatives. Definitive therapy should be based on antibiotic susceptibility results, although the clinician may be left without many alternatives if the isolate is XDR.

Charles and colleagues recently reported an outbreak of infection with XDR S. sonnei belonging to clade 5 in the United Kingdom.¹ Of the 72 patients identified, 97% were male, and, among those for whom the information was available, were predominantly MSM. For oral therapy, they recommended use of pivmecillinam (which is not available in the United States and for which they do not provide susceptibility data) and fosfomycin, to which the isolates were susceptible in vitro. Their recommended fosfomycin regimen for adults consisted of 3 g on day 1, day 3, and day 5 orally, but single agent fosfomycin therapy has the potential to rapidly select for resistance. Among parenteral antibiotics, the isolates were susceptible to ertapenem, meropenem, and temocillin (also not available in the United States). Among these, ertapenem would be the most convenient for outpatients since it is administered once daily.

REFERENCE

1. Charles H, Prochazka M, Thorley K, et al; Outbreak Control Team. Outbreak of sexually transmitted, extensively drug-resistant Shigella sonnei in the UK, 2021-22: A descriptive epidemiological study. Lancet Infect Dis 2022;22:1503-1510.