Following the 2004 tsunami that affected Indonesia, Sri Lanka and Thailand, the World Health Organization expressed concerns that the ensuing disarray might lead to outbreaks of cholera, malaria and dengue fever, to name a few threats. In the end, no such outbreaks occurred; relief and humanitarian efforts are credited for the favourable outcome.

In contrast, Haiti has multiple disadvantages at hand:

1) Before the earthquake, Haiti was a sad case for communicable diseases control

No city in Haiti ever had a water and sewerage system. Diarrheal diseases are common among children and often hit them before they can develop natural immunity. Typhoid fever remains endemic to Haiti. While cholera has not been encountered there so far, a few cases in the context of a contaminated water supply could cause havoc.

The population density in Haiti is the highest of all Latin American countries (crowding is synonymous with the spread of many infectious diseases), facilitating the spread of tuberculosis. Crowding also facilitates the spread of malaria, including the most deadly form: P. falciparum, and dengue fever (also transmitted by mosquitoes) in urban areas.

Poor vaccination coverage rates increase the risk of spread of measles, diphtheria and whooping cough in crowded settings. Respiratory infections such as pandemic H1N1 influenza spread also more easily in crowded settings, among those without access to medical care.

Other vaccine-preventable diseases such as tetanus are still encountered in newborn children. Fortunately, Haiti has been free of polio since 1994. Hepatitis B continues to spread in the absence of routine vaccination programmes.

Seven to 10 per cent of the sexually-active urban population is HIV-infected.  This group is at particularly greater risk of developing and spreading reactivated TB. The same applies to the 40% of children who are malnourished.

2) The earthquake just made a bad situation worse

In addition to all of the above, we have an additional issue: the administrative node of government has been destroyed. Even aid organization headquarters have been severely damaged. Moreover, aid workers cannot readily transport safe drinking water, water decontamination supplies or antibiotics / antimalarial medicines to many severely damaged areas of the country. Now, a civil insurrection and lack of a police force puts not only locals at risk but aid workers too.

Malnutrition will likely worsen for many in the coming days. Mother of infants, who should breastfeed in this circumstance, may see decreased milk production as a result of malnutrition and resort to formula feeding, with attendant risks of diarrheal disease for the infants with immature immune systems.

Improper disposal of corpses could lead to further contamination of the already unsafe water supply.

Many are now displaced into even more crowded and less hygienic environments than before, with improper waste disposal increasing the risk of spread of diarrheal disease.

An interrupted power supply increases the risk of stored food spoiling and becoming unsafe for consumption, while the lack of cooking fuel may increase the risks of inadequate cooking.

Inadequate laboratory diagnostic capabilities may require that many cases of dysentery occur before an outbreak is even noticed.

3) Even aid workers face risks

In contrast with the 2004 tsunami, aid workers face infectious diseases risks while in Haiti. Though they are protected from the worst of diarrheal diseases by access to bottled water, the segregated accommodation and bed nets will not entirely protect against mosquito-borne diseases cited above. In addition, the inadvertent consumption of local water may pose a risk of viral hepatitis (such as hepatitis A or E; a pre-travel vaccine does not exist for the latter), diarrheal disease, or typhoid fever. A domestic dog bite may pose a risk of rabies, and would need to be addressed promptly.

This is a dire situation that is quite different from the 2004 tsunami. As it turns out, the hackneyed aphorism of influenza pandemic planning -- “Plan for the worst, hope for the best” -- might have a more relevant application here.