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The burden and rigourness of typhoid fever infections caused by Salmonella enterica serovar Typhi is a substantial universal populace concern, particularly in developing countries (Demczuk, Finley, Nadon, Spencer, Gilmour & NG, 2010). It is a systemic infection primarily involving the alimentary tract (Christopher, 2002). It has been found that humans are the only natural reservoirs of S. Typhi, with contagion occurring through consumption of faecally contaminated food and water (Corner & Schwartz, 2005) or in other words, it occurs where there is substandard water supply and sanitation. It has been estimated by WHO that the annual global incidence of typhoid fever is at 0.3% (Demczuk et.,al, 2010). It has been estimated that annually 6, 00,000 deaths occur from enteric fever worldwide. S. Typhi infections may cause symptoms like bacteraemia, fever, headache, malaise, abdominal distress, diarrhoea and rose colored spots which contains the infecting organism (Chamberlain, 2006). Typhoid fever is preventable through vaccination prior to travelling to areas where typhoid is common and careful consumption of food. Treatment with appropriate antibiotics can also prevent complications.
S.typhi first of all invades the alimentary canal by ingestion then via the lymphatic system and the thoracic duct into the stream of blood. This first septicaemic phase leads to infection of the reticulo-endothelial system and the gall bladder. When the infection of the gall bladder occurs, there is discharge of organisms into the intestine, with heavy infection of the Peyer's patches and septicaemia- and the onset of symptoms (Sleigh & Timbury, 1998). Most of the symptoms which are caused by S.typhi can be ascribed to the inflammation caused by its lipopolysaccharide as it does not have any specific known endotoxins.
After an incubation period of 10-14 days, early symptoms like fever, headache and respiratory symptoms appear. Then, mild abdominal pain with either diarrhoea or constipation occurs. After that, fever increases in a stepwise fashion. Without treatment, the patient may eventually lapse into a stupor and the problem may persist for 4 to 6 weeks. A serious problem that is secondary invasion of the intestine from the gall bladder which can cause perforation of the intestine. In 15% of untreated cases, death may also occur.
Typhoid fever can be diagnosed by the laboratory tests to find the bacteria in the blood or faeces of an infected person. Illness is usually characterized by fever, loss of appetite, lethargy and change in bowel habit. Constipation is common in the initial stages but diarrhea can also occur. The diagnosis of enteric fever relies on the isolation of S.typhi from the patient. Specimens include faeces, blood and urine. The culture used for blood and urine is MacConkey medium in which enrichment and the selective media are not necessary. Blood culture is positive in more than 80% of patients in the first week of illness. Faeces should also be cultured especially at 2-4 weeks after onset of symptoms, when seeding of the kidneys and secondary infection of the intestine occurs. For faeces, indicator medium is used for non-lactose-fermenting colonies and selective and enrichment media for others (Sleigh & Timbury, 1998).
Identification can be done by the Biochemical reactions (API test). In this test, unlike other salmonellae, S.typhi produces no gas on fermentation of sugars. In serological identification, first of all preliminary diagnosis with salmonella polyvalent H and O antisera is done and after that final identification is done from where it is send to the Reference Typing Laboratory. Phage typing is also useful in identifying the different types of S.typhi for epidemiological identification into the source of outbreaks. Serum antibodies to the organisms can be detected by an agglutination test known as Widal test, but positive results must be interpreted with care where past exposure or vaccination are possibility. A fourfold rise in titre between acute and covalescent sera is diagnostic.
The salmonella bacterium resides in the human gut. The source of infection is the carriers or the cases that excrete the organism: excretion in faeces and less commonly in the urine. The infection continues for about two months after the acute illness. The route of infection is through the ingestion of water or food which is contaminated by sewage or via the hands of a carrier. Direct spread from case to case is rare. Only a small number of these bacteria can cause typhoid fever. This is the main reason that water-borne infection is common, despite the dilution of organisms.
The following are 'High risk' groups for developing Typhoid Fever:
Travelers with individualistic lifestyle and those are intending prolonged travel to areas where there is typhoid fever.
Former migrants from developing countries who are visiting their parent countries.
Those with no acid or low acid concentrations in their stomach such as post surgery or with regular use of antacids and medication to reduce stomach acidity.
Those with sever or ongoing disease may need particular advice about typhoid fever and where the intended travel is to be
Travelers to the Indian Subcontinent
Medical personnel, foreign aid workers and military personnel assigned in developing countries.
Outbreaks of typhoid fever are often explosive- sometimes involving large number of people. There are two main types of outbreak:
Water-borne: in which the organisms from the sewage acts as a carrier and pollutes the drinking water, e.g. the outbreaks in Croydon in 1937 and in Zermatt in 1963.
Food- borne: in which food becomes contaminated via polluted water or via the hands of the carriers. 'Typhoid Mary', possibly most famous carrier, worked as a cook in USA and caused number of outbreaks.
Tinned food may also become contagious during canning- the large outbreak in Aberdeen in 1964 was due to a tin containing corned beef which had been cooled in water contaminated by sewage; bacteria entered the can through tiny holes in the metal casing.
Shellfish often grow in estuaries, where the water may be contaminated by sewage: if it is eaten uncooked they may cause infection.
Milk or cream products, contaminated through the handling of the carriers, have caused outbreaks of typhoid fever. Other food products like meat, dried and frozen foods, dried coconut have also been responsible for infection.
Antibiotics are a type of medication effective in treating infections caused by bacteria based on signs and symptoms. Oral treatment with chloramphenicol, ampicillin, cotrimoxazole or ciprofloxacin is generally effective and should be maintained for 14 days to reduce the possibility. But resistive strains to above antibiotics have also been reported, particularly on Indian subcontinent (Lee & Bishop, 2010). For chronic carriers, long term therapy with ampicillin or ciprofloxacin may be effective but, if not, cholecystectomy (removal of gall bladder) may be warranted.
Chloramphenicol is a bacteriostatic antibiotic with wide spectrum of activity against gram-positive and gram negative cocci and bacillus. It binds to the 50S subunit of the ribosome and inhibits bacterial protein synthesis. Ampicillin is a broad spectrum semi-synthetic derivative of aminopenicillin that inhibits bacterial cell wall synthesis by binding to penicillin binding proteins and inhibiting peptidoglycan synthesis, a critical component of bacterial cell wall. Ciprofloxacin is a synthetic broad spectrum fluoroquinolone antibiotic which inhibits bacterial DNA gyrase, an enzyme essential for DNA replication. This agent is more active against Gram-negative bacteria than Gram-positive bacteria.
It is very difficult to eradicate S.typhii from the gall bladder. Antibiotic treatment is effective in curing some carriers, but still to some extent the infection persists and they become long-term permanent carriers. Promising results have been given by ciprofloxacin.
For the high risk groups, two effective typhoid vaccines: the oral live vaccine (Ty 21a) and the injectable Vi capsular polysaccharide vaccine is highly recommended. The live attenuated vaccine Ty 21a is a strain of S.typhi. It is indicated for those who travel to or living in areas where typhoid is an endemic and where the health care staff is at risk. It is administered in enteric-coated capsules orally in three doses on alternate days. Some mild adverse reactions may also persist like nausea, vomiting etc. This vaccine is quiet efficient but may be less durable. The other type of vaccine is a classic type killed vaccine which has now been replaced by other preparations but still it is being widely used. It contains heat killed phenol preserved suspension of S.typhi. It is injected and two doses need to be consumed 4-6 weeks apart and booster doses need to be taken every 3 years. In consuming this, some local and general reactions are common which vanishes after 36 hr from the onset.
In New Zealand, the injectable Vi Polysaccharide vaccine (Vi antigen) is recommended for all adult children over the age of 2 years travelling to areas where there is questionable sanitation. It is known that children under the age of 2 years may show a sub-optimal response to polysaccharide antigen vaccine. It gives approximately 70% protection against the disease. There are two products available in New Zealand and Australia: Typherix (GlaxoSmithKline) and Typhim Vi (MSD [NZ] Ltd). They are interchangeable.
The infection prevention and control team plays a vital role in preventing cross infection and prevention of hospital acquired infection. In order to ensure that infection is not caused, the surveillance team should keep highest level of vigilance in which phenomenon like proper aseptic techniques, hand hygiene practice should be followed. Furthermore, following preventive measures should be followed:
Wash and dry hands thoroughly after using the toilet or changing nappies. Hands should be washed for 20 seconds and dried for a further 20 seconds using a clean cloth or disposable towel.
Soiled clothing and linen should be washed with hot soapy water separately from that of other family members. Items such as face cloths and towels should be kept for personal use.
A person with Typhoid infection should avoid preparing food for others in the family until they are no longer infectious. In households where a person is recovering from typhoid, toilet seats, flush handles, wash basin taps and toilet door handles should be disinfected daily using a hypochlorite based solution. Ideally the solution should be in contact with the surface of the object for at least ½ hour.
Drink bottled, purified or carbonated water for drinking and cleaning teeth. Make sure that bought bottled water is appropriately sealed; regular water (sea level) should be brought to boiling point for one minute before it is safe to drink.
Avoid ice in drinks and remember that refreshing ice blocks and flavored ices may be made with contaminated water.
Foods should be thoroughly cooked and served piping hot. Be very wary of food sold by street vendors.
Avoid raw seafood and shellfish; even though they may have been preserved with vinegar, lemon or lime juice.
Choose raw vegetables and fruits that a person can peel himself. Avoid salads unless they have been made by own. Do not forget to wash hands with soap or hand cleaner first and not to eat the peelings.
Antimicrobial resistance surveillance is also a significant activity which needs to be practiced. Moreover, as the economies of the developing countries grow the sanitary conditions of currently typhoid- endemic countries will improve. Due to that, number o f typhoid fever cases will lessen. However, in order to expedite the elimination of typhoid fever, Member States and WHO will strengthen their power for typhoid fever surveillance by improving laboratory-based surveillance. Intersectoral collaboration at both national and international levels will be essential if the disease needs to be controlled in endemic countries.
In conclusion we have discussed in brief the organism- S.typhi, the laboratory diagnosis, its epidemiology, antibiotic treatment and finally the role of the infection control and prevention team in controlling the infection.