Healthcare Infection Prevention: Drug-resistant shigella outbreaks hit day care
Drug-resistant shigella outbreaks hit day care
Are exclusion policies fueling drug resistance?
Are day care centers exclusion policies inadvertently fueling antibiotic resistance in Shigella sonnei? That is the question Centers for Disease Control and Prevention epidemiologists are pondering after a spate of outbreaks in 2005.
Kansas, Kentucky, and Missouri reported increases in shigellosis cases associated with day care centers caused predominantly by multidrug-resistant (MDR) [i.e., resistant to ampicillin and trimethoprim-sulfamethoxazole (TMP/SMX)] strains of S. sonnei, the CDC reports.1
"In the day care-associated outbreaks of 2005, we had very high rates of resistance to both of those drugs," says Anna Bowen, MD, medical epidemiologist in the CDC enteric disease epidemiology branch. "Day care centers are settings where it is very easy to transmit shigella infections, and having highly resistant strains within that population is bad news for the children of our county."
In the United States, Shigella species cause an estimated 450,000 cases of gastroenteritis each year, mostly among children younger than 5 years old. S. sonnei is the most common species of laboratory-confirmed shigella infection in the United States and usually causes an acute, self-limited, diarrheal illness. During the past two decades, numerous outbreaks of S. sonnei infection have been associated with day care centers. Because few bacteria are required to transmit shigellosis from person to person through the fecal-oral route, shigellosis can propagate in settings with insufficient hygiene practices, the CDC reports.
Certain states, including the three states in the CDC report, require that children with shigellosis be excluded from day care centers until documentation indicates that they have submitted two consecutive stool specimens that do not yield S. sonnei. Thus — even though antibiotics may not be needed for most shigella infections — there may be parental pressure on providers to prescribe them in order to shorten the exclusion period and return the child to day care.
"This is fairly controversial," Bowen says. "On an individual patient basis, we would say you do not need antibiotics to treat this infection. It is self-limited, lasts a handful of days, and nearly everyone recovers completely without incident. However, the American Academy of Pediatrics [AAP] has issued guidelines that encourage states to develop policies to exclude children from day care centers when they are culture-positive for shigella in the interest of limiting transmission and trying to prevent outbreaks. These policies appear to encourage antibiotic treatment because that can shorten the course of illness and permit children to return to day care faster."
The unintended consequence in that policy is that it drives antibiotic resistance through repeated treatment courses in the pediatric population. CDC surveillance data for antimicrobial resistance among all S. sonnei isolates during 1999-2003 indicated that 80% of the isolates were resistant to ampicillin and 47% to TMP/SMX; 38% were resistant to both drugs. "In the two outbreaks described in this report, resistance to both ampicillin and TMP/SMX was 89%, complicating shigellosis treatment in these communities," the CDC warned.
Although ampicillin and TMP/SMX have been the drugs of choice for treatment of shigellosis, current resistance patterns limit the use of these antibiotics. Fluoroquinolones are an effective alternative for adults but are not approved by the Food and Drug Administration for shigellosis treatment in children younger than 18 years old. Macrolides, particularly azithromycin, also are recommended by the AAP for treatment of shigellosis. However, data about clinical effectiveness are limited, and no standardized guidelines for monitoring azithromycin resistance among shigellae are currently available.
Since an individual infection doesn't typically warrant antibiotic therapy, it remains somewhat unclear whether increasing antibiotic resistance will make shigella less of a "self-limiting" infection. However, in absence of sensitivity testing, physicians trying to treat shigella infections may end up prescribing ineffective antibiotics.
"It's hard for them to know whether they can still use those [standard] drugs or if they need to go one of the broader-spectrum, more expensive drugs that don't have FDA approval for use in children," Bowen says. "It is definitely a problem. If a child comes in with diarrhea and you culture, it would be several days before you get the antibiotic sensitivity results back. You either have to take a guess and start treating on the day they come in or wait until the cultures back. By that time, they have had already diarrhea for several days and the benefit of treatment might be questionable."
The CDC is in discussion with day care center and pediatric groups to try to solve the problem through such strategies as cohorting asymptomatic kids with shigella colonization rather than excluding them. However, state regulations in the three states cited in this story do not allow such measures. In the meantime, the emergence of multidrug-resistant shigellosis highlights the importance of prevention and rapid control of outbreaks, the CDC emphasizes. Appropriate hand-washing and diapering practices are critical in minimizing the transmission of shigellosis in day care centers. Scheduling hand-washing sessions on arrival at the day care center, before meals, or after playing outdoors; supervising hand washing among young children; and eliminating water play areas have been used to reduce the spread of shigellosis within day care centers and to the community.
"Every day care center should be paying careful attention to hand-washing and diapering practices, not just for shigella but for all of the other diseases that can be transmitted on hands," Bowen says. "We encourage all day care centers to focus on those basic hygienic practices, but we are struggling with what to do about the treatment and exclusion recommendations. We are trying now to review with AAP and within CDC how effective these [exclusion] policies are in reducing transmission and what their role is in driving the antibiotic resistance problems we are seeing."
Reference
- Centers for Disease Control and Prevention. Outbreaks of multidrug-resistant Shigella sonnei gastroenteritis associated with day care centers — Kansas, Kentucky, and Missouri, 2005. MMWR2006; 55(39); 1,068-1,071.