Typhoid fever causes - Environmental and social factors

Typhoid fever is the result of systemic infection mainly by S. typhi found only in man. The disease is clinically characterized by a typical continuous fever for 3 to 4 weeks, relative bradycardia with involvement of lymphoid tissues and considerable constitutional symptoms. The term "enteric fever" includes both typhoid and paratyphoid fevers. The disease may occur sporadically, epidemically or endemically.

(a) AGENT: S. typhi is the major cause of enteric fever. S. para A and S. para B are relatively infrequent. S. typhi has three main antigens O, H and Vi and a number of phage types (at least 80). Phage typing has proved a useful epidemiological tool in tracing the source of epidemics. S. typhi survives intracellularly in the tissues of various organs. It is readily killed by drying, pasteurization, and common disinfectants. The factors which influence the onset of typhoid fever in man are the infecting dose and virulence of the organism.

Man is the only known reservoir of infection, viz cases and carriers. 

(i) CASES: The case may be mild, missed or severe. A case (or carrier) is infectious as long as bacilli appear in stools or urine.

(ii) CARRIERS: The carriers may be temporary (incubatory, convalescent) or chronic Convalescent carriers excrete the bacilli for 6 to 8 weeks, after which their numbers diminish rapidly. By the end of three months, not more than 4 per cent of cases are still excreting the organisms; and by the end of one year, the average carrier rate is around 3 per cent. 

Persons who excrete the bacilli for more than a year after a clinical attack are called chronic carriers. In most chronic carriers, the organisms persist in the gall bladder and in the biliary tract. A chronic carrier state may be expected to develop in 2 to 5 per cent of cases. A chronic carrier may excrete the bacilli for several years (may be as long as 50 years) either continuously or intermittently. 

The famous case of "Typhoid Mary" who gave rise to more than 1300 cases in her life time is a good example of a chronic carrier. Faecal carriers are more frequent than urinary carriers. Chronic urinary carrier state is often associated with some abnormality of the urinary tract.

The primary sources of infection are faeces and urine of cases or carriers; the secondary sources contaminated water, food, fingers and flies. There is no evidence that typhoid bacilli are excreted in sputum or milk.

(a) Age: Typhoid fever may occur at any age. Highest incidence of this disease occurs in the 5-19 years of age group. Prospective population-based surveillance in some Asian urban slum areas has shown that in the age group 5-15 years, the annual incidence of blood culture-confirmed typhoid fever may reach 180-494 per 100,000. In some of these areas, pre-school-age children less than 5 years, show incidence rates similar to those of school-age children. After the age of 20 years, the incidence falls probably due to acquisition of immunity from clinical or subclinical infection.

(b) Sex: More cases are reported among males than females, probably as a result of increased exposure to Infection. But carrier rate is more in females.

(c) Immunity: All ages are susceptible to infection. Antibody may be stimulated by the infection or by immunization; however, the antibody to the somatic antigen (O) is usually higher in the patient with the disease, and the antibody to the flagellar antigen (H) is usually higher in immunized individuals. 

Serum antibodies are not the primary defences against infection, S typhi being an intracellular organism, cell- mediated immunity plays a major role in combating the infection. Natural typhoid fever does not always confer solid immunity; second attacks may occur when challenged with a large oral dose. Among the host factors that contribute to resistance to S. typhi are gastric acidity and local intestinal immunity.

Enteric fevers are observed all through the year. The peak incidence is reported during July-September. This period coincides with the rainy season and an increase in fly population. Outside the human body, the bacıllı are found in water, ice, food, milk and soil for varying periods of time. Typhoid bacilli do not multiply in water; many of them perish within 48 hours, but some may survive for about 7 days. 

They may survive for over a month in ice and icecream. They may survive for up to 70 days in soil irrigated with sewage under moist winter conditions, and for half that period under drier summer conditions. Food being a bad conductor of heat, provides shelter to the bacilli which may multiply and survive for sometime in food. 

Typhoid bacılli grow rapidly in milk without altering its taste or appearance in anyway. Vegetables grown in sewage farms or washed in contaminated water are a positive health hazard. These factors are compounded by such social factors as pollution of drinking water supplies, open air defecation and urination, low standards of food and personal hygiene and health ignorance. Typhoid fever may therefore be regarded as an index of general sanitation in any country.

Usually 10-14 days. But it may be as short as 3 days or as long as three weeks depending upon the dose of the bacilli ingested.

Typhoid fever is transmitted via the faecal-oral route or urine-oral routes. This may take place directly through soiled hands contaminated with faeces or urine of cases or carriers, or indirectly by the ingestion of contaminated water, milk and/or food, or through flies.

Fig. 1 shows the dynamics of transmission There are numerous sources of infection and many vehicles of transmission, each making its own contribution to the total magnitude of the problem The situation is rendered more complex by the web of social, cultural and economic factors which determine the quality of life of the people.

The onset is usually insidious but in children may be abrupt, with chills and high fever. During the prodromal stage, there is malaise, headache, cough and sore throat, often with abdominal pain and constipation. The fever ascends in a step-ladder fashion. After about 7-10 days, the fever reaches a plateau and the patient looks toxic appearing exhausted and often prostrated. 

There may be marked constipation, especially in early stage or "pea soup" diarrhoea. There is marked abdominal distention. There is leukopenia and blood, urine and stool culture is positive for salmonella. If there are no complications the patient's condition improves over 7-10 days. However, relapse may occur for up to 2 weeks after termination of therapy.

During the early phase, physical findings are few. Later, splenomegaly, abdominal distension and tenderness, relative bradycardia, dicrotic pulse, and occasionally meningismus appear. The rash (rose spots) commonly appears during the second week of disease. The individual spot, found principally on the trunk, is a pink papule 2-3 mm in diameter that fades on pressure. 

It disappears in 3-4 days. Serious complications occur in up to 10 per cent of typhoid fever patients, especially in those who have been ill longer than 2 weeks, and who have not received proper treatment. Intestinal haemorrhage is manifested by a sudden drop in temperature and signs of shock, followed by dark or fresh blood in the stool. 

Intestinal perforation is most likely to occur during the third week. Less frequent complications are urinary retention, pneumonia, thrombophlebitis myocarditis, psychosis, cholecystitis, nephritis and osteomyelitis. Estimates of case-fatality rates of typhoid fever range from 1 per cent to 4 per cent; fatality rates in children aged children (0.4%). In untreated cases, the fatality rates may rise to 10-20 per cent.