Prevention of Cholera

In the West nowadays a patient with cholera will remain a sporadic case. In developing countries one case can lead to several secondary cases. It is not necessary to wear special masks, aprons or gloves, but washing hands (hospital staff, family, visitors) should be obligatory. The contamination of clothing and bedding is unavoidable. Boiling in water for five minutes is sufficient for disinfection. Mattresses and blankets can be dried in the sun. It is better to do this before washing them, to prevent infection of the washing area.

After surviving cholera a patient is probably immune for more than 3 years. No cross-immunity between V. cholerae O1 and V. cholerae O139 is seen, although they produce the same toxin. Immunity relies on antibodies in the intestinal lumen (the bacteria are not invasive). Babies which are being breast-fed receive protective antibodies in their mother’s milk. Vaccination with dead V. cholerae bacteria (IM administration) does not lead to the formation of protective antibodies in the intestinal lumen. Advice to vaccinate was discontinued in 1972 by the WHO [World Health Organisation]. New oral vaccines are being tested. Vaccination, mass chemoprophylaxis and cordon sanitaire (= restrictions on travel and trade) are not effective in preventing or limiting outbreaks.

Mass chemoprophylaxis is not effective because (1) the infection spreads faster than the organisation of drug distribution, (2) the effect of a drug only lasts 2 days, after which re-infection may occur, (3) the whole population needs to be treated simultaneously and people should then be isolated and (4) it is difficult to convince asymptomatic people to take a drug. Selective chemoprophylaxis of nearby contact persons can be given, certainly if there appear to be multiple secondary cases (the role of monitoring is important here).

Correct eating and drinking habits, safe stool habits and personal hygiene are the most effective means for individuals to limit their risk of cholera. Improved sanitation is the pre-eminent method of eliminating cholera and many other faeco-orally transmitted infections. This is directly linked, however, to the degree of poverty in a region. Boiling drinking water is often difficult since fuel may be scarce and expensive. Since a significant proportion of Vibrio cholerae can adhere to plankton, the drinking water can be filtered through a fine cloth, which removes both plankton and a lot of bacteria in a single operation. This is of course less effective than obtaining water from a clean pipe or pump, but it is cheaper. Chlorination of drinking water may be important (piped water or via water trucks). This is difficult to accomplish in rural areas. Chlorination is much less effective if the water is turbid due to organic debris.

Eating raw fish, shellfish (e.g. oysters, mussels) and crustaceans (such as crabs, shrimps) should be avoided. Washing hands is important for transmission control within a household. Infected faeces should not be disposed of in a poorly functioning drain (hospital: e.g. in pit with unslaked lime). When large groups of people come together (funerals, festivals, etc.) there should be latrines with facilities for washing hands.

An attempt must be made to trace the source of small, local outbreaks (see John Snow). Infected water is the chief suspect in a sudden, local epidemic, while in isolated cases the cause should be sought in infected food. This is of course not an absolute rule. Food cooked by street vendors and in restaurants poses specific problems. Flies probably play an underestimated part in transmission, but their numbers also reflect the sanitary conditions in a region.

The following points should be emphasised during information campaigns:

• Drink only clean water (boiled or chlorinated)

• Cook food completely and eat it while it is hot

• Avoid uncooked food, unless it can be peeled

• Wash hands after a bowel movement

• Wash hands before preparing food

• Wash hands before eating

• Correct use of a good latrine (also for children)

• With correct treatment cholera is rarely fatal

• If cholera is suspected medical help should be sought immediately

• In diarrhoea, give plenty of fluids (e.g. ORS)

• No cholera-vaccination (unless better vaccines are developed in the future)

In case of an epidemic, it is important to have a large stock of IV rehydration fluid available as well as the means of preparing large amounts of oral rehydration fluid. Normally such buffer stocks should be stored at various strategic points. The stocks for cholera treatment should not be segregated in storage, but should be rotated during normal use to avoid allowing large amounts to run out of date. As soon as an epidemic is suspected, use as much oral rehydration as possible so that stocks of the IV solutions last as long as possible. Cholera beds should be made ready. In a normal epidemic an attack rate of 0.2% can be taken as a rule of thumb (i.e. 200 cases can be expected in a population of 100,000). This is useful for estimating the size of stocks that will be needed. Sometimes the attack ratios are higher (e.g. the Rwanda-Zaire border in 1994).

During an epidemic one should consider

1. clean drinking water in sufficient amounts,

2. sanitary provisions (latrines + hand washing with soap ± hand desinfection with hypochlorite solution),

3. treatment of the patients

4. direct contact persons of the patient (e.g. mother of a child) may take chemoprophylaxis, but mass prophylaxis is not advisable.

5. The risk for a traveller who observes elementary hygiene is very small (1/500,000).

Category: Medical Subject Notes , Microbiology Notes