Shigella - Microbial Food Poisoning

Shigella

Shigella microbes comprise non-motile, gram- negative rods that have the same characteristics (morphological and biochem-ical) as E. coli. The common species of shigella responsible for food poisoning include Sh. dysenteriae, Sh. flexneri, Sh.boydii, and Sh. sonnei. In general, Shigella outbreaks are morelikely to be caused by S. sonnei species in developed countries, while S. dysenteriae and S. flexneri are more frequently found in developing countries. The most severe form of infection is associated with S. dysenteriae serotype; case fatality rates range from 5 to 15%.

Source

·      Fruits

·      Vegetables

·      Milk.

Fruits (stewed apples), vegetables (potato salad, mashed potatoes), tossed salad and milk products are the commonest vehicles. Epidemics due to watermelon ingestion have been reported.

Children (6 months to 5 years) are at highest risk for devel-oping shigellosis; especially children in daycare centers where the illness can spread rapidly. Also, individuals in custodial care centers, international travelers, homosexual males, and those living in houses with poor sanitation.

Toxin

·              Though Sh. dysenteriae (type I) elaborates an enterotoxin, it appears to be much less important in pathogenesis than the ability of the bacillus to penetrate and multiply in colonic mucosa.

Incubation Period

About 1 to 7 days (usually 2 days). 

Clinical Features

Individual presentation varies with some patients demonstrating only minor symptoms, while others may suffer true dysentery with high fever, tenesmus, nausea, crampy abdominal pain, and profuse diarrhoea.

·      Large, watery (relatively odourless) stools, followed by bloody diarrhoea in 24 hours.

·      Abdominal cramps, tenesmus.

·      Fever.

·      Cough, rhinorrhoea.

·      Vomiting (uncommon).

·      The WBC count is usually <10,000/mm3, with a marked shift to the left; the band count is usually very high.

·      Complications:

o     Arthritis: Reiter’s syndrome can occur as in the case of salmonellosis (vide supra).

o     Toxic neuritis, convulsions.

o     Conjunctivitis.

o     Parotitis.

o     Intussusception (in children).

o     Haemolytic uraemic syndrome.

Diagnosis

·              Monitor serum electrolytes.

·              A CBC with differential may be useful in diagnosis.

·              Stool and ingested food should be cultured.

·              Faecal polymorphonuclear neutrophil leukocytes are present in many cases of shigellosis.

Treatment

·      Patients with significant toxicity, dehydration, electrolyte disturbances, or a history of poor compliance should be admitted for IV fluid therapy, and occasional antibiotic therapy.

·      Antibiotic therapy must not be resorted to as a routine measure. It is indicated only in severe cases, or in elderly patients and infants. While antibiotic resistance is a common problem, most cases still respond to nalidixic acid or norfloxacin. However, quinolone antibiotics must be used with caution in children.

The following antibiotics are currently recommended by the World Health Organization for the treatment of Shigella dysenteriae serotype (Sd1) which is commonly seen in developing countries such as India: ampicillin, trimethoprim-sulfamethoxazole, nalidixic acid, pivmecillinam, ciprofloxacin, norfloxacin, and enoxacin, though resistance is common with ampicillin, trimethoprim-sulfamethoxazole, and nalidixic acid.

·      Anti-motility agents (loperamide or diphenoxylate with atropine) are likely to make the illness worse and are not recommended.