Shigella Blog

The CDC in MMWR, reports that in May 2012, the Los Angeles County Department of Public Health’s Acute Communicable Disease Control Unit and Environmental Health, Food, and Milk Program investigated an outbreak of shigellosis associated with a private bridge club. This investigation documented the first known transmission of Shigella sonnei with decreased susceptibility to azithromycin in the United States.

Cases were defined as an illness clinically compatible with shigellosis in a patient or S. sonnei isolated from stool of a person with an epidemiologic link to the bridge club during May 22–26, 2012. Investigators attempted to interview all bridge club workers and members who had visited the bridge club during the week of May 22; they collected stool specimens from workers who handled food and from workers and members with diarrhea who had not already submitted a stool specimen for culture at a health facility. Thirty-nine cases were identified among club members with diarrhea and four among club workers; of the four workers, two, including one who handled food, reported no symptoms. The average age of affected persons was 75.3 years (range: 54–98 years); 55% were female. Among those with symptoms, the duration of illness averaged 5.9 days (range: 1–14 days). Common symptoms included diarrhea in 95% of patients, abdominal cramps in 70%, and fever in 56%. Thirty-one (72%) persons sought medical care, and 10 (23%) were hospitalized. No specific exposures implicated a source for the outbreak.

Among the 43 cases, 14 were culture-confirmed; 10 isolates underwent pulsed-field gel electrophoresis (PFGE), yielding indistinguishable patterns. Four isolates submitted to CDC’s National Antimicrobial Resistance Monitoring System (NARMS) displayed resistance to streptomycin, sulfisoxazole, tetracycline, and trimethoprim-sulfamethoxazole. Unlike most Shigella isolates tested by NARMS, these isolates also showed elevated azithromycin minimum inhibitory concentrations (MICs) of >16 µg/mL and harbored a plasmid-encoded macrolide resistance gene, mphA.

CDC’s PulseNet identified two additional isolates indistinguishable from the outbreak PFGE pattern. One was from a man in Pennsylvania aged 23 years who had visited Los Angeles in April, and the other from a man in Hawaii aged 53 years who visited Los Angeles during April and May; both men were hospitalized with diarrhea. Neither case was epidemiologically linked to the bridge club or to each other.

Although sporadic cases of shigellosis caused by Shigella strains with increased azithromycin MICs have occurred, this is the first outbreak documented in the United States and might indicate increasing circulation of such strains. Illnesses in this outbreak tended to be severe; however, the affected population was much older than the general U.S. population. Clinical management of such illnesses is likely to be complex; although azithromycin currently is recommended for treatment of infections caused by multidrug-resistant Shigella, options for alternative treatment among children with such infections primarily include parenteral antimicrobial medications.

Abilene Texas has seen a rise in Shigella cases since August, officials with the Abilene-Taylor County Public Health District report. Young children have been affected especially heavily.

Eighty cases have been reported since the first week of August, compared with about six cases per year on average.

A previous major outbreak occurred in 2002, when more than 200 cases were reported. By contrast, no cases were reported during 2010. Actual numbers will be higher, since not everyone experiences symptoms goes to a health care provider.

“Shigellosis is an infection of the intestines that causes diarrhea,” the report reads. “It is usually a mild, self-resolving illness (meaning the body will fight off the infection without treatment), and most people recover completely within 4 to 7 days.

Shigella is highly contagious and often begins with a victim swallowing something contaminated by the feces of an infected person. This usually happens when the infected person fails to properly wash hands after a bowel movement, then touches the hands or food of another person. Even a person without symptoms can pass on the bacteria.

Prevention methods include:

• Hand-washing after bathroom visits, diaper changes or handling of pets or soil. Hands should be washed for at least 20 seconds using running water and soap. Hand sanitizer may be used as a substitute.

• Children should wash hands frequently, with young children doing so under adult supervision.

• Washing hands after diaper changes is especially important if the child has diarrhea.

Since May, the Douglas County Health Department has investigated 50 confirmed cases of Shigella sonnei (shigellosis) infection, including four that involved hospitalizations. In eight of the nine previous years, Douglas County reported 31 or fewer cases.

Symptoms of shigellosis can range from loose, watery stools with no other symptoms to bloody diarrhea with fever and cramps. People experiencing diarrhea should remain home from school or work until at least 24 hours after their symptoms stop. Anyone with diarrhea should not prepare food or drink for others.

“Hand washing is absolutely critical to controlling any disease that involves diarrhea,” Health Director Dr. Adi Pour said. “It is especially important to wash your hands with soap for at least 20 seconds after changing diapers or using the bathroom, since it takes only a small exposure to pass along the disease.”

Forty-one percent of these recent shigellosis cases involved children less than 5 years old and 29 percent were between 5 and 9 years old. Most of the cases, 62 percent, have been associated with child care settings.

It is also important for anyone who has been sick to stay out of swimming pools and water parks for a week after they have recovered. Most of the recent Douglas County cases are linked to day care facilities, but swallowing pool water is another way shigellosis may be transmitted.