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Salmonella typhi

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Typhoid – still endemic in many parts of the world

This is the causal organism of typhoid (or enteric) fever, representing a more serious form of Salmonella infection than the other salmonellae.

Growth and Control Survival Inactivation (CCPs and Hurdles) Clinical Notes Reservoirs / Sources

Temperature

Minimum 7°C, growth greatly reduced at <15°C. Maximum 45°C. Optimum 35-37°C.

Water Activity

Minimum 0.94, optimum 0.99, maximum >0.99.

pH

Minimum 3.8, optimum, 7-7.5, maximum 9.5. The minimum pH is influenced by other factors such as the acid present, and the presence of nitrite etc.

Atmosphere

Can grow in the presence or absence of air. Growth under nitrogen is only slightly less than that under air. Grows at 8-11°C in the presence of 20-50% CO2.

Temperature

Survival can be quite good, for example the organism was viable for 190 days when inoculated onto chocolate biscuits, and for 230 days on sweets. S. typhi can survive for 4 days in shellfish stored at 10-13°C, and in ice for in excess of 90 days.

Viable but Non-Culturable (VNC) Cells

This organism is thought to undergo transition to the VNC state in water.

Water Activity

Inactivated within 1 day when exposed to 30% NaCl.

Sanitisers / Disinfectants

Treatment of S. typhi -contaminated bean sprouts with 200 mg/l sodium hypochlorite only reduced the count by 1.5 log cycles (i.e. ineffective).

Don’t forget to read the disclaimer!

Incubation

7-28 days (average 14)

Symptoms

Fever, malaise, anorexia, spots on trunk. These occur commonly with pea-like diarrhoea or constipation. Patients may become delirious. Recovery is slow, taking from 1 to 8 weeks. Hospitalisation rate estimated at 75%, case fatality rate 0.4%.

Toxins

Toxins are not produced in foods.

At Risk Groups

In non-endemic areas children between 0-5 years are at the greatest risk.

Treatment

Quinolone and cephalosporin antibiotics may be used. Vaccines are available.

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