COMMENTARY

Multidrug-Resistant Shigellosis: An Emerging Sexually Transmitted Infection

Anna Bowen, MPH, MD

Disclosures

October 10, 2016

Editorial Collaboration

Medscape &

Multidrug-resistant (MDR) Shigella infections may be spreading among your adult patients in a way that you might not have considered: through sexual transmission. Although shigellosis is most commonly transmitted from person to person among young children and their caretakers,[1] many recent reports have documented shigellosis outbreaks and increased risk for MDR shigellosis among men who have sex with men (MSM).[2,3,4,5] Unprotected oral-anal sex, digital-anal contact, and other sexual practices that expose patients to feces can transmit shigellosis.

Antimicrobial-resistant shigellae currently appear to be more prevalent among MSM than among other groups of people in the United States,[4] but because of Shigella's extremely low infectious dose, transmission to other populations is likely.[5,6] Clinicians can help prevent MDR shigellosis strains from spreading by maintaining a low threshold for obtaining stool cultures and antimicrobial susceptibility testing among patients suspected of having shigellosis, and counseling such patients during the initial clinical encounter about steps they can take to minimize transmission to their loved ones and the community.

Shigellosis

Shigellosis is caused by a group of gram-negative bacteria called Shigella and is characterized by watery or bloody diarrhea, abdominal pain, tenesmus, occasionally fever, and malaise for 4-7 days. An estimated 500,000 cases occur in the United States annually.[7]The incubation period is typically 1-4 days after exposure but may last up to 7 days. Shedding of Shigella bacteria in feces typically stops within 1-4 weeks after symptoms cease; long-term carriage is uncommon.

Shigellosis is transmitted through the fecal-oral route and is very contagious; a small inoculum (10-200 organisms) is sufficient to cause infection.[8] Transmission of Shigella occurs through the following mechanisms:

  • Person-to person contact, including sexual activity;

  • Ingestion of contaminated food, beverages, or recreational water; and

  • Hand-to-mouth transfer after touching fomites.

Oral-anal sex (anilingus or "rimming") is a documented risk factor for shigellosis among MSM,[9] but other practices, such as digital-anal contact (fisting), anal sex, oral-penile sex, and oral-vaginal sex are also likely to confer risk.

High-Risk Groups

Compared with the general US population, MSM appear to be at higher risk for shigellosis, including infection with strains that are not susceptible to azithromycin, ciprofloxacin, and ceftriaxone, the recommended treatments for both children and adults with shigellosis.[4,10,11] Furthermore, HIV-positive persons can have more severe and prolonged shigellosis.[12]

However, because of the low infectious dose, all populations are at risk for shigellosis. Shigellosis outbreaks in childcare, elementary school, homeless populations, and other community settings can be large, protracted, and difficult to control.[5,6,13,14,15]

Diagnosis and Testing

If you suspect shigellosis, especially among adult men, obtain a stool culture and request antimicrobial susceptibility testing of clinical isolates. If your laboratory uses culture-independent diagnostic tests (CIDTs) for enteric infections, request a stool culture and antimicrobial susceptibility testing when patients are diagnosed with shigellosis by CIDT. Information about antimicrobial susceptibility is important when considering treatment options because shedding of shigellae in feces may be prolonged if the patient is treated with an antimicrobial medication to which the isolate is resistant.

Although most clinical laboratories have not traditionally performed azithromycin susceptibility testing for Shigella isolates, guidance for testing and interpreting azithromycin minimum inhibitory concentrations among shigellae was released in January 2016.[16] Your state public health laboratory may be able to assist with such testing if it is not available at your clinical laboratory.

Local regulations may require confirmation that shigellae are absent from one or more convalescent fecal specimens before a patient with shigellosis can return to childcare or work in a sensitive occupation (eg, childcare, food service); convalescent fecal cultures may also be useful among patients with MDR Shigella infections to determine whether shedding of Shigella in the feces has stopped, and to allow more tailored counseling about prevention.

Treatment

Most patients recover without treatment within 5-7 days of symptom onset. If a patient requires treatment with an antimicrobial medication, select the agent on the basis of results of antimicrobial susceptibility testing. Uncomplicated infections are typically treated for 3-5 days, depending on the antimicrobial agent.

Prevention of Shigellosis

All patients with shigellosis should be counseled that shigellosis is very contagious but that they can take simple measures to protect others:

  • Meticulous handwashing with soap and clean, running water, particularly after using the toilet or changing the diaper of a child with shigellosis.

  • Refrain from preparing food for others while ill, and wash hands carefully before preparing food for others after recovery. Professional food handlers may be required to comply with additional local public health codes before returning to work.

  • Staying out of pools and other swimming venues until the diarrhea stops. Diapered children should not swim for 1 week after diarrhea stops.

  • Keeping ill children out of childcare facilities and other group settings until after diarrhea has stopped and local public health regulations permit them to return to childcare settings.

Patients may not be aware that shigellosis can be transmitted through sexual activity. Counsel adult patients that they can reduce sexual transmission of shigellosis through:

  • Avoiding sex while ill and for 2 weeks after recovery. Patients can shed shigellae in their feces for 1 or 2 weeks—and, rarely, for months—after symptoms cease.

  • When resuming sex or having sex with someone whose diarrhea history is unknown:

    • Wash hands, genitals, and anus before and after sex.

    • Use barrier methods during sex. Barrier methods include condoms for mouth-to-penis, penis-to anus, and penis-to-vagina sex; dental dams or condoms that have been cut open for mouth-to-anus or mouth-to-vagina sex; and latex gloves for anal fingering or fisting.

    • Wash sex toys after each use, and wash hands after touching used sex toys.

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