ATLANTA - Early infection-control measures, including active surveillance and limited epidemiologic investigation, may prevent nosocomial transmission of group A streptococcus (GAS) infections, according to a recent Centers for Disease Control and Prevention (CDC) report.
"With the advent of good antiseptic techniques, you really don't see very many of these outbreaks," said Sharon Balter, MD, medical epidemiologist at the CDC. "However, there are rare occasions when asymptomatic carriers can transmit group A strep despite proper antiseptic techniques."
GAS is rarely a cause of surgical site or postpartum infections. Approximately 15 postoperative or postpartum GAS outbreaks have been reported since 1965, which were attributed to asymptomatic carriage in health care workers (HCWs), according to the report. The report, which appeared in a recent issue of the Morbidity and Mortality Weekly Report, describes two nosocomial outbreaks of GAS infection in Maryland and California during 1996 to 1997.
Broken cutaneous or mucosal barriers facilitate invasive infection after GAS exposure, causing surgical and obstetric patients to be particularly susceptible to infection. GAS is a common cause of pharyngitis and uncomplicated skin and soft tissue infections. However, it can cause serious invasive infections, such as necrotizing fasciitis and streptococcal toxic-shock syndrome (STSS), and could lead to death.
"Most group A strep infections are relatively mild things like strep throat," Balter said. "Only in rare cases does it become invasive or life-threatening."
GAS is isolated from less than 1% of surgical-site infections and 3% of infections after vaginal delivery. The anus is the usual site of asymptomatic carriage among HCWs, although vaginal, skin and pharyngeal carriage have been implicated.
Studies have suggested that airborne spread of the organism is possible even if a throat culture proves negative, according to Balter.
"Even properly gowned and gloved health care workers who are rectal and vaginal carriers can shed GAS into the environment," she said.
When a case is detected, active prospective and retrospective surveillance for additional cases should be instituted, according to Balter. This includes examining medical and laboratory records to identify previous infections, as well as collecting and storing isolates from currently infected patients.
Limited epidemiologic investigation should follow, which includes limited screening of HCWs. For postpartum patients, all HCWs who performed vaginal examinations before delivery or were present at the delivery should be screened.
In cases of postoperative GAS infection, screening should include those who changed dressings on open wounds of the infected patient.
According to the report, cultures of the nostrils, throat, vagina, rectum and skin of the HCWs should be taken. Workers may return to work pending culture results. Any HCW with a positive culture should refrain from patient contact for 24 hours after the start of antimicrobial treatment.
If surveillance identifies additional patients or HCWs infected with GAS, the isolates should be typed to identify the strain. If the isolates are the same and a carrier has not been identified, screening should expand to include workers who had less direct patient care.
"It's much less likely for infants to become infected because they don't have skin breaks," Balter said. "But it certainly could happen."
In the case of the Maryland outbreak, none of the infants born to the women infected with GAS were symptomatic and were not tested for GAS infection. "There was no reason to think they had become infected," she said.
The CDC also recommended obtaining cultures from household contacts of implicated carriers to identify and treat potential reservoirs for reinfection. To prevent recurrence, carriers should be monitored with periodic surveillance cultures for one year after treatment.
The first outbreak occurred in Maryland during July 1996 to August 1997. Seven patients with postpartum GAS infections were identified in an unnamed hospital. Two more obstetric patients were found to be infected with GAS upon examination of microbiology records.
Three of 198 HCWs from the labor and delivery or postpartum wards developed positive cultures, although only one matched the patients' strain, emm type 77. This worker's wife also developed a positive culture. All three HCWs, as well as the one worker's wife, were treated for GAS, and were followed for one year, which proved negative. The Maryland outbreak yielded no deaths nor any additional cases.
The unnamed California hospital's outbreak occurred during Dec. 23, 1996, to Jan. 1, 1997, and reported three patients infected with STSS, emm type 1, with indistinguishable restriction fragment length polymorphism.
One surgeon, who performed surgery on the patients, was the only HCW who had direct contact with the three patients in the operating room. He began self-initiated penicillin therapy before adequate cultures could be taken. Rifampin was added following adequate culturing. Culture's taken from those in his household were negative.
Another surgeon performed surgery on one of the patients and assisted in the other two patients' surgeries. Both surgeons were restricted from patient care until 10-day therapy was completed, and no other postoperative GAS infection developed thereafter.
Examination of microbiology records revealed that no other cases of postoperative GAS infection occurred for the six months before the outbreak. Forty-one health care workers who worked in the operating room, pre- and postoperative areas on the days of surgery of the three patients were screened for GAS. Only one worker grew a positive throat culture, emm type STNS5.
Two of the three patients in the California hospital outbreak died as a result of their infections.
For more information:
- CDC. Nosocomial group A streptococcal infections associated with asymptomatic health care workers - Maryland and California, 1997. MMWR 1999;48(8):163-6.
- Kolmos HJ, Svendsen RN, Nielsen SV. The surgical team as a source of postoperative wound infections caused by Streptococcus pyogenes J Hosp Infect 1997;35:207-14.
- Schaffner W, Lefkowitz LB Jr, Goodman JS, et al. Hospital outbreak of infections with group A sptreptococci traced to an asymptomatic anal carrier. N Engl J Med 1969;280:1224-5.
You can express your views on this article, or other relevant themes, in the Infectious Diseases in Children Specialty Forums.