Food as source of outbreaks of group A streptococcal disease
A recent report described an outbreak of scarlet fever in a primary school (1). The outbreak investigation concluded that person to person transmission was the main source of transmission. This does not explain the simultaneous illness in a large number of children (n=29) occurring within 5 days and ongoing transmission over a month despite rigorous exclusion of cases from school. The investigation did not take into account that the source of every outbreak of group A streptococcal disease reported in the literature so far has been contaminated food with seven outbreaks of food borne streptococcal disease reported from the European Union since 1970 (2). A previous outbreak report of group A streptococcal pharyngitis in an elementary school found that attendees who ate macaroni and cheese prepared by a cook with a hand wound infected by the outbreak strain had a significantly higher risk of group A streptococcal disease (3). Other reports of outbreaks of group A streptococcal disease reported as a source salad or sandwiches with hard boiled egg being the most likely ingredients associated (2, 4, 5). For early abortion of a school outbreak it is essential to stop school dinners until a source within the school kitchen is excluded. The secondary cases of transmission in the families of infected children observed by Lamden were most likely due to airborne transmission by droplets aerosolised by sneezing and coughing (6). During an outbreak such secondary cases can be prevented by immediate exclusion of all children with features of respiratory tract infection from school with offer of immediate treatment with penicillin rather than waiting for culture confirmation in each case.
References: 1. Lamden KH. An outbreak of scarlet fever in a primary school. Arch Dis Child doi: 10.1136/adc.2010.189944. 2. Falkenhorst G, Bagdonaite J, Lisby M, Madsen SB, Lambertsen L, Olsen KEP, Molbak K. Outbreak of group A streptococcal throat infection: don't forget to ask about food. Epidemiol Infect 2008; 136: 1165-71. 3. Farley TA, Wilson SA, Mahoney F, Kelso KY, Johnson DR, Kaplan EL. Direct inoculation of food as the cause of an outbreak of group A streptococcal pharyngitis. J Infect Dis 1993; 167: 1232-5. 4. Lancefield RC. Streptococcus in the salad. Lancet 1969; 2: 157. 5. Berkley SF, Rigau-Perez JG, Facklam R, Broome CV. Foodborne streptococcal pharyngitis after a party. Public Health Rep 1986; 101: 211- 5. 6. Bar-Dayan, Y, Bar-Dayan Y, Shemer J. Food-Borne and air-borne streptococcal pharyngitis-a clinical comparison. Infection 1997; 25: 12- 15.
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