BOSTON - The first outbreak of invasive group A streptococcus (GAS) to occur among day care and school children resulting from varicella complications was recently investigated by state and federal health officials.
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In February, Boston Public Health Commission officials received reports of two cases of invasive GAS and varicella infection among 14 children attending the same child care center classroom in suburban Boston.
That same month a 4-year-old girl with varicella was taken to a local hospital with swelling, tenderness, warmth and redness over her left upper arm and shoulder.
The girl was admitted to the hospital with a diagnosis of cellulitis and received doses of intravenous clindamycin, but her symptoms did not improve. She then underwent surgical exploration for possible necrotizing fasciitis (NF) and received a total fasciotomy of her left arm. Cultures of tissue specimens obtained at surgery grew GAS, serotype M1T1.
Thirty-nine children, 1 to 4 years of age, were enrolled in the center. The children had been divided into three classrooms by age group. The groups were separated throughout the day except for two hours of outdoor play. To assess the prevalence of GAS carriage associated with the center, throat swab specimens were obtained from all the children, their household contacts and all center employees.
Cases of GAS infection were identified by review of hospital records and telephone interviews with physicians. History of strep throat as well as GAS carriage was found among students and some family members. None of the teachers nor parents were found to have varicella, said officials from the Centers for Disease Control and Prevention (CDC).
"It wasn't clear who introduced either infection into the community," said Stephanie H. Factor, MD, epidemiologist in the division of bacterial and mycotic diseases at the CDC. "But invasive GAS can be a very difficult pathogen to eradicate, not in the sense of a Typhoid Mary where people carry around the pathogen and spread it, but they can keep the bacteria alive."
Surveillance studies indicate that among the known risk factors for invasive GAS are previous trauma, cardio-pulmonary disease, cancer and steroid use, diabetes, immunosuppression, being 65 years or older and being Native American.
Investigators at the CDC still cannot say for certain if incidences of invasive group A strep are increasing nationwide, but they do know it can occur in clusters. Los Angeles suffered a GAS cluster outbreak two years ago; Seattle recorded an NF cluster recently; and this past winter Cincinnati had a GAS outbreak.
"There are no indications that GAS outbreaks favor one region of the country over another," said Benjamin Schwartz, MD, chief of the childhood and respiratory diseases branch at the CDC. "But we can say for certain that it favors certain individuals over others."
Massachusetts and CDC investigators used four case definitions to categorize the GAS status:
Of the 14 classmates of the first two patients, three had strep throat and two were carriers. Two of the three available isolates (one obtained from a child with strep throat and one from a carrier of GAS) were serotype M1T1. In addition, two cases of possible GAS infection were identified: one with an infected varicella lesion and the other with cellulitis of the leg; however, cultures were not obtained from the lesions, said Factor.
Among the 25 children in the other classrooms, one had scarlet fever, serotype M1T1, and one was a carrier of GAS of a different serotype. From the 92 household contacts, three had strep throat, but their isolates were not available for serotyping. Carriage of GAS was present in two people (one was serotype M1T1; the other was a different serotype). Of the 13 child care center workers, only one person was a GAS carrier. The child with scarlet fever and the household contact carrier of serotype M1T1 were both siblings of classmates of the first two patients.
Risk factors for GAS infection among the classmates of the first two infected patients were identified from responses by parents on self-administered written questionnaires. All nine cases of test-confirmed (by culture or rapid-antigen test) and possible GAS infection occurred in people with varicella infection.
Of the 14 classmates of the first two patients, a total of 12 were found to be susceptible to varicella at the start of the school year; one had a previous history of varicella, and one had been vaccinated against varicella.
The first cases of varicella occurred on Jan. 15; of the other 11 susceptible children, the onset of varicella in 10 occurred during Jan. 29-Feb. 1. Of these, seven were identified with GAS infection or carriage and two had onset of possible GAS disease two weeks following the onset of varicella.
Of the 11 children who were not receiving antibiotics and whose GAS status was test-confirmed, seven spent more than 30 hours a week at the day care center and had documented GAS infection or carriage, compared with no infection for the other four children who spent less than 30 hours a week at the center.
A total of 112 environmental surfaces were cultured to assess the possible role of fomites in disease transmission. These surfaces included handles and other sites that a child was likely to grip and any toy that a child was likely to place in his or her mouth. Of the 112 samples, six pieces of plastic toy food were positive for GAS; five were serotype M1T1.
Varicella vaccine was recommended and provided free for all children, center staff and household contacts considered susceptible to the pathogen. To prevent additional cases of GAS infection, prophylactic antibiotic therapy was recommended for all carriers of GAS and all classmates of the first two patients, regardless of culture results.
"Though health officials in Boston were quick to respond, one of the suggestions made in the report was that this particular outbreak might have been prevented through pre-emptive use of varicella vaccines," said Factor.
Invasive GAS disease is a severe and sometimes life-threatening infection in which the bacteria affects unusual areas of the body, such as the blood, deep muscle and fat tissue and the lungs.
Of the approximately 8,000 invasive GAS cases each year in the United States, the CDC estimates that 5% to 10% are complicated by NF and 5% to 10% by staphylococcal toxic shock syndrome (STSS). Death occurs in close to 20% of patients with NF and 50% who contract STSS.
In contrast, there are several million cases of strep throat and impetigo annually. The greatest number of chickenpox cases occur in late winter and spring with adults suffering the highest rate of complications and death.
For more information:
- CDC. Outbreak of invasive group A streptococcus associated with varicella in a child care center. MMWR. 1997;46:944-8.
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