An outbreak of shigellosis in a child care institution in Queluz, Portugal – 1995

A Suspiro1, L Menezes2

1 Public Health Doctor, Health Authority

2 Public Health Doctor

From: Saùde em nùmeros, 1996; (11) 1: 5-7

The introduction of shigella into a child care centre carries a high risk of secondary spread from person to person within the centre (1). We report an outbreak of shigellosis in early 1995 that affected 99 children, 17 of their relations, and seven workers in a day care institution for children under 10 years of age. The health authority closed the institution for five days to control the outbreak and all the families at risk were contacted in order to give an appropriate antimicrobial drug to all those affected.

The outbreak occurred in late February and early March. Those who became ill suffered diarrhoea with blood, mucus, and pus and high fever, cramps, and malaise. Three patients were admitted to hospital. Shigella sonnei was isolated from the stools of nine cases tested at random and the three children admitted to hospital. The strain isolated in each case was resistant to tetracycline and co-trimoxazole.

The outbreak occurred in two waves (figure). In the first wave 65 cases were reported in five days. The attack rate differed with age: two out of 48 kindergarten children (aged less than 3 years) became ill (4.1%) and 65 out of 222 older children and adults (28.4%). It seemed likely that a common source of infection was responsible (figure). The children and adults had eaten lettuce and home made mayonnaise prepared with raw eggs, but no leftover food was available for testing.

In the second wave of the outbreak 41 cases occurred in a pattern compatible with spread through faecal oral transmission from convalescent cases to susceptible people in the institution.

It appeared that co-trimoxazole, with which cases had been treated in the early phase, had not prevented the second wave of infection. At this point the institution was closed for five days during which 82 cases were given antibiotic treatment, mostly amoxycillin to which the organism was sensitive. Subsequently a random sample of 43 patients submitted faecal specimens, all of which were negative. In addition to these two measures, asymptomatic carriers were excluded among foodhandlers.

No control groups from the institution or the community were investigated and no analytical study was conducted to investigate the possibility that the first wave of cases was associated with a food vehicle. The investigation of this outbreak highlighted the risk of secondary transmission after a foodborne infection if hygiene is neglected. Although shigellosis is usually a self limiting disease, when it occurs in an institution for very young children or others unable to manage their own personal hygiene, special care should be taken both with hygiene measures and the administration of antimicrobial drugs to patients. It is likely that the organism’s resistance to common antibiotics and the initial failure to exclude convalescent cases from the institution contributed to the spread of infection (2).




(1) Benenson AS. Control of Communicable Disease in Man. 15th edition, 1990, American Public Heath Association.

(2) Tauxe RV, Johnson KE, Boase JC et al. Control of day care shigellosis: a trial of convalescent day care in isolation. American Journal of Public Health. 1986, 76(6):627-30.

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