TORONTO Children with chickenpox have among the highest risks for invasive group A streptococcal (GAS) disease, researchers reported recently.
For children younger than 10, the investigators estimated that those who have chickenpox are at 39 times higher risk for invasive GAS infections than those who do not have chickenpox, according to researchers. Among children younger than 10 who have chickenpox, the attack rate for invasive GAS infections was 4.4 per 100,000 cases of chickenpox.
Elderly people and people with underlying chronic illnesses such as cancer or heart disease also are at high risk, researchers reported.
Because of a resurgence in reports of severe GAS disease in recent years, Donald E. Low, MD, and colleagues launched a study to identify all cases that occur in Ontario, beginning Jan. 1, 1992, and to characterize those cases and define risk factors for infections. In the New England Journal of Medicine article, they described their findings based on data gathered from Jan. 1, 1992 to Dec. 31, 1993.
During that period, they identified 323 people who suffered invasive GAS infections, which translated into an annual incidence of 1.5 cases per 100,000 population. Children younger than 10 and people older than 74 had the highest rates.
Fifty-six percent of patients had underlying chronic illnesses. Necrotizing fasciitis (NF) occurred in 20 people (6%) and toxic shock occurred in 42 (13%).
Overall, 15% of people died, but the death rate was 29% among people older than 64 years and 81% among those with toxic shock.
In addition, 14% of infections were acquired in hospitals. Four percent occurred in nursing home residents.
Researchers defined invasive GAS infections as those in which Streptococcus pyogenes bacteria were isolated from a normally sterile anatomic site.
According to study findings, people who have HIV infection, heart disease, cancer or diabetes have a risk for invasive GAS infections that is 10, 8.5, 7.5 and 4.1 times, respectively, than people without those illnesses.
Low told Infectious Diseases in Children that invasive GAS disease is increasing in incidence and severity in Ontario.
In 1992, Ontario had 139 cases of invasive GAS illness, eight of which were accompanied by NF. By comparison, the province had 267 cases of invasive GAS illness in 1995, of which 30 were accompanied by NF.
"We don't know yet whether that [increase in the incidence of NF] reflects the type of strain which has come into the community which maybe is more apt to cause necrotizing fasciitis," said Low, who is chief of the microbiology department at Mount Sinai Hospital, an affiliate of the University of Toronto.
Although other investigators have suspected an association between development of invasive GAS infections and prior use of nonsteroidal anti-inflammatory drugs (NSAIDS), Low and colleagues did not try to identify such a link. They detected no association, however, between use of NSAIDS and severity of illness in people with invasive GAS infection, Low said.
Low and colleagues also examined the risk of infection among household contacts of people with invasive GAS infections. Of 152 household contacts of 46 patients with invasive GAS infections, 18 (12%) carried S. pyogenes in their throat. All isolates were the same strain as that of the index patient. Household contacts were more likely to be colonized if they were children and if they had four or more hours of contact daily with the index patient, according to the study. The Low team estimated that household contacts of people with invasive GAS infections have a risk for invasive GAS infection that is 200 times greater than the general population.
In Ontario and Quebec, antibiotic prophylaxis is recommended for family members of people stricken with streptococcal toxic shock or NF. This approach, which is controversial in the United States, is difficult to implement, Low said.
For more information:
- Davies HD, McGeer A, Schwartz B, et al. Invasive group A. streptococcal infections in Ontario, Canada. N Engl J Med 1996;335:547-54.
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