Bacillary Dysentery Shigellosis

Organism Bacillary dysentery is due to Shigella invading the bowel. The species and strains of Shigella are numerous. There are four main groups:

• S. dysenteriae with 12 serotypes;

• S. flexneri with 14 serotypes;

The most severe are S. dysenteriae and the least severe S. sonnei, with S. flexneri being the most common in endemic areas. Another form of bloody diarrhoea is due to enteroinvasive and enterohaemorrhagic E. coli, particularly serotype 0157.

Clinical features Bacillary dysentery presents as an acute diarrhoeal illness with blood in the stools, more acute and severe than amoebic dysentery. In mild infections, blood may be absent with a similar presentation to gastroenteritis. In severe cases, the stools are a mixture of pus and blood, and tenesmus is common. Fever accompanies the illness and nausea or frank vomiting can occur. Severity is determined by the strain of organism and age of the person, with a moderate mortality in the very young and very old.

Diagnosis If bacteriological facilities permit, the organism should be identified, typed and sensitivity determined. A suitable transport medium is Carey Blair. Where this is not possible, a simple epidemi-ological investigation may provide sufficient information to indicate the mode of transmission.

Transmission is by the faecal-oral route with either food or water as the main vehicle carrying the infection. Bacillary dysentery can occur in small outbreaks amongst families, suggesting food as the mode of transfer. Seasonal epidemics coinciding with the arrival of the rains indicate water-borne spread. Flies can be important in hot dry months when garbage accumulates and mas sive fly breeding takes place. Only 10-100 organisms are required to produce the disease.

Carriers can be important and sporadic epidemics in institutions might indicate a food handler with unsanitary habits.

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