1) Pattern of contamination
The reservoir of Salmonella typhi is strictly human. Transmission may be inter-human by direct contact with an infected person, or indirectly by swallowing food contaminated during cooking by a sick person (or a healthy carrier ) or by swallowing food (shellfish, seafood, raw vegetables) contaminated by fecally soiled water.

Some people infected by typhoid (whether treated or not), remain chronic carriers with intermittent germ excretions in faeces, and, so, potentially contagious.

2) Epidemiology
Like all illnesses with oro-fecal transmission, typhoid fever is predominantly found in settings with poor sanitation and hygiene standards and hits especially developing countries in Asia, Africa or Latin America. The distribution pattern of this illness at world level is quite similar to that of hepatitis A (brought about by the same factors).

It is prevalent in all parts of the world, and depends on whether water is pure or not. There is a seasonal peak from August through October, mostly as people return home after a stay in hot countries (70 % of the cases are 'imported').

3) Clinical aspects
After an incubation period ranging from one to three weeks, the disease classically develops in two stages :

- The invasion stage (1st week) associates a rise in temperature occuring by steps (40° C with a dissociation of the pulse), headaches, asthenia*, insomnia, anorexia-type digestion disorders, nausea and abdominal cramps with constipation or diarrhoea. Myalgia* and arthralgia* are also likely to appear. This stage may also appear suddenly right away in a gastroenteritis clinical picture that may simulate an acute surgical picture, particularly among small children.
- The stage of physical state (week 2) involves fever which levels off between 39° and 40° C (dissociated pulse) and emission of diarrhoea-type faeces (classically 'melon-juice' diarrhoea). A state of drowsiness appears and develops into serious forms of prostration (typhoid state). Cases of splenomegalia* are common. Infection may also cause an erythema* rash on the chest.

Complications may occur such as perforation or hemorrhage of the intestine, or myocarditis*, osteomyelitis*, encephalitis*. Such complications are caused by the release of endotoxins during the salmonella lysis* .

4) Diagnosis
The germ is found in the blood in 60% of cases only. It may be found uncontinually in faeces and urine.

The standard blood check-up only shows non-specific abnormalities : rise in the number of 'leucocytes', white blood cells, sometimes decrease in the number of 'thrombocytes', blood platelets signalling severe forms.

The search for 'antibodies' pitched against the salmonella's 'antigens' O and H ( Widal's test) does not enable to tell a new infection from a former and cured infection. Other tests are available that are more specific, yet carrying them out is difficult in a third-world country.

5) Treatment
After the patient has been hospitalized and isolated, the treatment current applied usually consists of second-generation 'Fluoroquinolone' or 'Ceftriaxone'. Rehydration of the patient, often intravenously, is imperative to compensate for the liquid losses secondary to the diarrhoea. A treatment for fever may sometimes be needed.

6) Testing and prevention
- It is important to comply with the classical health measures : frequently wash hands with water and soap, especially each time you go to the toilet and before handling food.
- Within the patient's family circle: need to screen all the healthy carriers by means of coprocultures to avoid the infection disseminating, mostly among people working in the agro-processing industry, in collectivities of small children as well as among the health-care personnel.
- Advice to people travelling in endemic regions : make sure you only consume cooked food and capsulated mineral water or previoulsy boiled or purified water by adding chlorinated lozenges and frequent washing of hands with water and soap especially every time you leave a toilet and before you handle food.
Besides, there exists an efficient vaccine against Salmonella Typhi (Typhim Vi). Protection is secured for 15 days following vaccination (to be renewed every three years).

Glossary
Asthenia : state of fatigue and exhaustion
Myalgia : muscle pains
Arthralgia : joint pain
Splenomegalia : enlargement of the spleen
Erythema : blotchy skin
Myocarditis : acute inflammation of the myocardium
Myocardium : tissue of the heart muscle
Osteomyelitis : infection of bones through the bloodstream
Encephalitis : inflammation of a more or less significant part of the brain
Lyse : Disagregation of some substances o organisms through the effect of a physical, chemical or biological agent.

Sources : Institut Pasteur
Institut français de veille sanitaire CHU de Rouen