​Key Messages​

• Extensively drug-resistant (XDR) Shigella infections have been rising across California for several years, with a sharp increase in cases in 2024 to date.
• In the first five months of 2024, 12% of Shigella isolates sequenced have been identified as XDR.
• Twenty-one percent of isolates among males 25-34 years of age were identified as XDR.
• ​Among adult male XDR patients with available data, 75% self-identified as men who have sex with men (MSM).
• Healthcare providers should tailor shigellosis antibiotic treatment to available antimicrobial susceptibility testing (AST) data, and counsel patients at increased risk of Shigella infection (see below) on prevention and risk reduction practices.
• Clinical laboratories should perform complete antibiotic susceptibility testing that includes azithromycin, ciprofloxacin, ceftriaxone, trimethoprim-sulfamethoxazole [TMP-SMX], and ampicillin, on available Shigella isolates as resources allow.
• Local health departments (LHDs) should monitor local XDR Shigella trends and continue reporting XDR isolates. In addition, they should make community stakeholders aware of this rise in XDR Shigella, particularly for MSM populations. 
  

​Situational Update

The California Department of Public Health (CDPH) has been monitoring an increase in reported extensively drug-resistant (XDR) Shigella infections (shigellosis), particularly since 2024 to date. From January through May 2024, 12% (118/978) of California Shigella isolates were reported as XDR based on whole genome sequencing, compared to 6.8% in 2023 (78% increase). Males aged 25-34 years old, the group with the highest rates of shigellosis in California, also had the highest percentage of isolates identified as XDR from January through May 2024 (21%). Among adult male patients with XDR Shigella infections, 75% self-identified as MSM. The 118 reported XDR cases in California from January through May 2024 are likely an underestimate of total statewide burden of XDR Shigella infections, given that most people with Shigella infections do not seek healthcare or receive testing. 

Background

Shigellosis

Shigellosis is an acute enteric infection by Shigella spp. that is an important cause of domestically acquired and travel-associated bacterial diarrhea in the United States (U.S.). Shigella bacteria are transmitted by the fecal-oral route, directly through person-to-person contact including sexual contact, and indirectly through contaminated food, water, and other routes. Shigella​ are easily transmitted because of the low infectious dose (as few as 10–100 organisms), and outbreaks tend to occur among people in close-contact settings [1].

Historically, shigellosis has predominantly affected young children (aged 1–4 years) in the U.S. More recently, there has been an increase nationally in antibiotic-resistant Shigella​​​ infections among adult populations [2], especially:

• Gay, bisexual, and other men who have sex with men (MSM)
• People experiencing homelessness (PEH)
• International travelers
• People with HIV (PWH)
  

Shigellosis usually results in an inflammatory diarrhea that can be bloody and may also lead to fever, abdominal cramping, and tenesmus. Most people with diarrheal illness, including shigellosis, require only supportive care and fluid replacement. For those who do require antibiotic therapy, antibiotic choice should be guided by antimicrobial susceptibility testing (AST) performed by a clinical lab.
Antibiotics may be indicated to:

• Shorten the duration of illness (by about 2 days), or
• Reduce the likelihood of transmission:
• during outbreaks,​
  
• in institutional settings,
• from food handlers,
• to immunocompromised persons or those being treated with immunosuppressive drugs, and
• ​to people living with HIV.

In the U.S., recommended empiric antibiotics include azithromycin, ciprofloxacin, or ceftriaxone. Ampicillin or TMP-SMX are recommended as alternative treatments for susceptible strains [3].

XDR Shig​​​ella​

CDC defines XDR Shigella bacteria as strains that are resistant to all commonly recommended empiric and alternative antibiotics — azithromycin, ciprofloxacin, ceftriaxone, trimethoprim-sulfamethoxazole (TMP-SMX), and ampicillin. XDR Shigella isolates included in this summa​​ry have been identified based on whole genome sequencing performed at select public health laboratories in California and identification of resistance genes.

Given the treatment challenges posed by XDR Shigella, CDPH encourages clinical laboratories to perform complete AST (azithromycin, ciprofloxacin, ceftriaxone, trimethoprim-sulfamethoxazole (TMP-SMX), and ampicillin) on all available Shigella​ isolates and report results to local health jurisdictions and providers in a timely manner. XDR Shigella strains can spread antibiotic resistance genes to other enteric bacteria.

Clinicians treating patients infected with XDR strains have limited antibiotic treatment options and should tailor treatment if necessary to available antibiotic susceptibility testing data. CDPH asks healthcare professionals to be vigilant about suspecting and reporting cases of XDR Shigella infection to their local health department (LHD), asking about social and behavioral risk factors for Shigella transmission, and educating patients and communities at increased risk about risk reduction and infection prevention practices. CDPH will continue to monitor XDR Shigella infections and track Shigella isolates with unique or worrisome antibiotic susceptibility patterns and genetic resistance markers.

Epidemiology of XDR Shigella in California

Since first detected in California in 2017, XDR Shigella has been increasing in prevalence. By 2022, 3.2% of Shigella isolates were XDR and further increased to 6.8% in 2023.  From January through May 2024, 12% (118/978) of California Shigella isolates were reported as XDR based on whole genome sequencing performed at public health laboratories. Thirty-seven percent (44/118) of XDR isolates were reported from Southern California and 44% (52/118) from the San Francisco Bay Area. Shigella sonnei isolates accounted for the largest percentage (78%), followed by Shigella​ flexneri (22%).

The median age of patients with XDR Shigella infections was 38 years (range 1-84 years), with 52% of patients between 25 and 44 years old. Most (86%) patients were adult males (n=102). Among 89 patients with available information on race and ethnicity, 53% (n=47) were non-Hispanic white, 21% (n=19) Hispanic, 11% (n=10) non-Hispanic Black or African American, 7% (n=7) non-Hispanic Asian or Pacific Islander, and 7% (n=6) other or multi-racial. Among adult males with XDR Shigella​ infections and available information, 75% (48/64) self-identified as MSM. Among all patients with available information, 9% (8/94) were persons experiencing homelessness and 10% (9/88) reported international travel.​

​

XDR Shigella​ bacteria are defined as resistant to azithromycin, ciprofloxacin, ceftriaxone, trimethoprim-sulfamethoxazole, and ampicillin.

Includes Shigella isolates sequenced in California PulseNet Laboratories (California Department of Public Health Microbial Diseases Laboratory, Los Angeles County Public Health Laboratory, Orange County Public Health Laboratory, Santa Clara County Public Health Laboratory); data are preliminary and based on presence of resistance genes and mutations found in whole genome sequences of bacterial DNA.

Recommendations

Recommendations for Healthcare Professionals

Diagnosis

• Consider shigellosis in the differential diagnosis of acute diarrhea, especially for patients at higher risk for Shigella infection, including:
• Young children
• MSM
• People experiencing homelessness
• International travelers
• Immunocompromised persons
• People with HIV (PWH)
• If shigellosis is suspected,
• Ask the patient about relevant exposures and social history, including sexual activity (and gender of sex partners), housing status, and international travel.
• When ordering diagnostic testing for Shigella, stool culture is preferred for patients who will require antibiotic treatment.
• If a culture-independent diagnostic test (CIDT) is performed instead of culture and Shigella bacteria are detected, request on sample submission that the clinical laboratory perform reflex culture.
• CIDTs (such as PCR panels) cannot provide information on antibiotic susceptibility or resistance profile.
• If a culture is positive for Shigella, order antibiotic susceptibility testing (AST) to inform antibiotic selection. Ensure AST covers complete antibiotic profile for Shigella (azithromycin, ciprofloxacin, ceftriaxone, trimethoprim-sulfamethoxazole, and ampicillin)​
  

Clinical Management

• To date, there are no CDC or CDPH recommendations for treating XDR shigellosis in the United States.
• Most patients recover from shigellosis without antibiotic treatment.
• CDPH and CDC recommend using antibiotics only when clinically indicated as overuse can contribute to the development of antibiotic resistance.
• Healthcare providers treating XDR shigellosis should consult with a specialist knowledgeable in treating antibiotic-resistant bacteria to determine the best treatment options.
• Use AST results to guide antibiotic treatment selection, when available.
• Encourage patients to inform you if symptoms do not improve within 48 hours after beginning antibiotics.​​

Considerations for Sexual Health

Increases in drug-resistant Shigella infections have been described among adult men and may be associated with transmission among MSM. Cases of shigellosis co-occurring with other sexually transmitted infections (STIs), including HIV, have been described among MSM [4]. For additional considerations, see the CDPH Shigellosis Among MSM webpage.

Clinicians caring for patients with shigellosis should:

• Take a sexual history if shigellosis is confirmed or suspected.
• People with acute proctitis and concern for sexually transmitted proctocolitis or enteritis should be tested for other STIs, including HIV, mpox, syphilis, gonorrhea, and chlamydia at exposed sites [4].
• Encourage all persons with shigellosis to notify their household contacts and sex partners and urge them to monitor for symptoms of shigellosis and seek medical evaluation and treatment if symptomatic. Exceptions to this practice include circumstances posing a risk for intimate partner violence [5].
• Counsel patients to abstain from sexual contact for 2 weeks following resolution of diarrheal symptoms.
• Educate high risk patients on shigellosis prevention strategies;

• Ask sexual partner(s) if they have or recently had diarrhea. If so, WAIT to have sex until at least 2 weeks after the diarrhea resolved. 
• Wash hands, genitals, and anus with soap and water before and after sexual activity.
• Wash sex toys and douching materials with soap and water after each use
• Wash hands after touching sex toys, douching materials, external and internal condoms, dental dams and any other item that might have been in contact with vagina or anus.
• Avoid practices that might cause oral contact with feces during sex, such as oral anal sex (rimming) or having unwashed hands or toys near or in mouth after contact with anus or genitals.
• Consider using condoms or dental dams during oral-genital sex and oral-anal sex to reduce contact with fecal matter. Consider using latex gloves during anal fingering or fisting. ​