ICPs must move quickly when Group A strep strikes
May 1, 1999 7 minutes read
ICPs must move quickly when Group A strep strikes
Outbreaks linked to asymptomatic HCW
Two days before Christmas in 1996, a previously healthy 28-year-old woman underwent a parathyroidectomy at a hospital in California. Six days later, she was dead. Such is the sudden severity of invasive infection with Group A streptococcus (GAS), which in this case was linked to an asymptomatic surgeon who performed the procedure.
Two other surgical patients were infected in the outbreak, including a previously healthy 56-year-old woman who underwent a subtotal thyroidectomy performed by the same surgeon and assistant on Dec. 30, the Centers for Disease Control and Prevention reports.1 Discharged Dec. 31, the second patient was found dead in her home later that day. A third patient, a previously healthy 57-year-old woman who also underwent a subtotal thyroidectomy, was routinely discharged the day after her Dec. 30 procedure by the same surgical team. On Jan. 1, 1997, she sought care at the emergency department and was admitted to the ICU in shock, with respiratory failure and renal impairment. It would take a full month of hospitalization before she recovered enough to be discharged. All three patients were infected with the same GAS strain, which caused streptococcal toxic shock syndrome.
The outbreak underscores that infection control professionals must act quickly when strep strikes if subsequent nosocomial cases are to be prevented. At the same time, the CDC also reported a markedly different nosocomial strep outbreak in Maryland in which cases were undetected in part because they were spaced out over more than one year. In light of the outbreaks, the CDC issued updated guidelines that essentially expand upon previous recommendations and underscore the importance of prompt investigations. (See guidelines, p. 64.)
Immediate steps after identification of the first strep case include looking for other infected patients and culturing the health care workers involved with the index case to search for an asymptomatic carrier, says Sharon Balter, MD, a medical epidemiologist in the CDC respiratory diseases branch.
"In California, it is possible that is an example of actually doing a fairly rapid investigation," she says. "It was over an eight-day period with Christmas and New Year’s [included]. Clearly, if they hadn’t done what they did, it is possible there would have been more deaths. The message that we were trying to get across is that doing [a rapid investigation] can prevent more cases."
A review of microbiology records at the California hospital — which was not named by the CDC — revealed no episodes of postoperative GAS infection during the six months before the outbreak. The CDC found that "surgeon A" was the only health care worker who had contact in the operating room with all three patients. Nasopharyngeal, throat, rectal, and vaginal cultures were obtained from the 41 staff members who worked in the operating room and the pre- or postoperative areas on the days of surgery for the patients. All cultures were negative except for a throat culture from an orderly that grew GAS of a different strain from the patients. Surgeon A received self-initiated penicillin on Jan. 2, before adequate cultures were obtained. The CDC did not describe that aspect of the case in any detail, but Balter says the surgeon likely acted to protect subsequent patients and other contacts.
Culture first, antibiotics second
"I think that most health care workers are horrified by the idea that they could be transmitting something," she says. "We would recommend that you should culture first and then do antibiotics. It is really a quick thing to do the culturing. Again, part of why we put this out is to give physicians, infection control practitioners, and others working in hospitals some kind of guidance. The advantage of culturing first is that then you have an answer. It would be extraordinarily rare to find two carriers."
Still, given the virulence of the strain, both surgeon A and assisting surgeon B were restricted from patient care until each had completed a 10-day course of penicillin and rifampin. Throat cultures from surgeon A’s household contacts were negative. No further postoperative GAS infections occurred.
The patient exposures presumably occurred during the surgical procedures, but no breaches in infection control or sterile techniques were reported or detected in observing subsequent procedures by surgeon A, Balter adds. Indeed, vaginal and rectal carriers of strep have been shown to shed the pathogen into the air even if fully gowned and gloved, she notes. In one case, a health care worker who stocked OR carts — but never actually participated in procedures — caused a series of mysterious strep infections until investigators found she was shedding the organism from the scalp.2
"So there clearly is some airborne transmission of this disease even if you are properly gowned and gloved, and even if you are a only a rectal or vaginal carrier," Balter says. "It is extremely rare — there are fewer than 20 reports of this that I could find in the literature."
There is little that could have been done to prevent the California outbreak, given the asymptomatic state of carriage and strep’s ability to slip through infection control precautions, adds Allison McGeer, MD, director of infection control at Mount Sinai and Princess Margaret Hospitals in Toronto, and a clinical researcher with the Ontario Group A Streptococcal Group.
"This is not a setting in which the surgeon could be blamed," she tells HIC. "There is nothing you could control. With Group A strep, you can get into trouble even if your usual infection control practices are excellent."
Indeed, it is not uncommon for subsequent patients to already be infected by the time the first case is identified, she adds.
"It’s just possible that if [they] moved instantly, and people weren’t on holiday, and surgeons and other people happened to be [available], then you might in that circumstance have prevented the second and third cases," she says. "But it would have been really tough."
Though the CDC recommends screening known carriers for one year after an outbreak, any additional attempt to routinely screen groups of health care workers for strep would be fruitless, McGeer says.
"The only common-sense thing that health care workers sometimes [forget] is that if you have a strep throat, you shouldn’t be working until you have been on antibiotics 24 hours," she says. "But beyond that, Group A strep is everywhere, and there is no way of predicting when you are going to pick it up or who is going to become a carrier. Even short-term carriage of Group A strep in adults is rare. In most cases when we have looked at health care workers, the colonization rate at any one point in time has been 1% or less, and that is not permanent carriage. So the frequency with which people become carriers of Group A strep for more than a few days is really low."
In contrast to the sudden onset of the California outbreak, strep infections due to an asymptomatic health care worker also can occur sporadically in a pattern that is difficult to recognize. Such was the case with the aforementioned outbreak at a Maryland hospital, where seven patients were infected with postpartum GAS infections from July 1996 to August 1997, the CDC reports.
"That is a prolonged period of time for seven patients," McGeer notes. "This highlights the need to recognize that two cases three months apart may not be separate cases. With Group A strep, you need to keep your eyes and ears open."
In the Maryland investigation, an infection was defined as GAS isolated from any nonpharyngeal site in a patient whose symptoms began more than 12 hours after admission to hospital A between January 1996 and September 1997. A review of the hospital’s microbiology records for all nonpharyngitis GAS cultures during the study period identified two additional postpartum cases. No cases were identified on other wards. Of the nine case patients, seven had endometritis. Two of those had sepsis, and one developed hypotension and required admission to the intensive care unit. One patient developed postcesa rean delivery wound infection, and another had a urinary tract infection. No patients died.
Exposure to one health care worker — whose job title the CDC did not identify — was strongly associated with infection in a case control study. Overall, swab specimens were collected and cultured from the throat, rectum, vagina, and skin of 198 workers who worked on the labor and delivery or postpartum wards during the outbreak period.
Mass culturing sometimes is necessary
"In Maryland, because it had gone on so long, there was clearly a need to act fast and you had to culture a lot of people," Balter says. "That is not necessarily the ideal way to do it — to go in and mass-culture 200 people in a week. But when something has gone on a while, there is pressure to do that."
Three health care workers had positive cultures, but only a rectal isolate from the health care worker implicated in the case control study was identical to the strain from one of the patients. The health care worker’s wife, who was asymptomatic, had positive rectal and vaginal cultures for the same strain. The two were treated with oral vancomycin and rifampin. Surveillance cultures of the health care worker have remained negative, and the hospital has had no additional cases.
In dealing with such an outbreak, it is important to establish some prospective surveillance if the full range of cases is to be identified, Balter adds.
"In many cases, postpartum patients with fever are not cultured; they are just given antibiotics," she says. "If you do that, you will miss a lot of cases. So alert the physicians that they really need to culture febrile patients and alert the labs to notify you immediately if there are additional cases."
References
1. Centers for Disease Control and Prevention. Nosocomial group A streptococcal infections associated with asymptomatic health-care workers — Maryland and California, 1997. MMWR 1999; 48:163-166.
2. Mastro TD, Farley TA, Elliot JA, et al. An outbreak of surgical-wound infections due to group A Streptococcus carried on the scalp. N Engl J Med 1990; 323:968-972.
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