Tent cities in Haiti combined with existing poor conditions give cholera exactly the conditions it needs to flourish.
Cholera is caused by a water-borne bacterium called Vibrio cholerae. According to the US Centers for Disease Control (CDC), the strain causing deaths in Haiti came from south Asia, either in contaminated water or food, or through the arrival of an infected person.
The disease can travel the globe in this way and causes little trouble where water, sanitation and hygiene control are in good shape. But it came to Haiti at a time when the island was desperately vulnerable.
Crowded conditions, poverty and poor sanitation were already the norm in parts of Haiti, but the earthquake gave cholera exactly the conditions in which it can flourish, with people forced to live in tent cities, taking their water from the same rivers where others wash and defecate.
Unfamiliarity with the disease is a problem in Haiti. Fear brings patients to the overcrowded hospitals with unrelated symptoms, while nursing staff, who are in very short supply, have to be taught to recognise and treat cholera and overcome their own fear of infection.
Once the infection takes hold, it is hard to keep in check. People in Haiti move about, travelling to market, to visit friends or get work.
Logistics are difficult
The old idea of a “cordon sanitaire” to prevent the movement of infection is not practicable, said Kate Alberti, an epidemiologist working with Medecins sans Frontieres in Haiti.
“If you close the official channels people find another way to cross,” she said. The arrival of cholera in the capital was no surprise.
Fighting the epidemic is hard. The first priority is to treat people, which needs to be done in cholera treatment centres away from other sick people in hospitals.
Massive efforts are under way but it is hard to find even land to erect a shelter in earthquake-devastated Port-au-Prince. The logistics are the hardest part — cholera is relatively easy to treat with antibiotics if people arrive in time.
But stopping infection spreading is a huge challenge. Before the disease arrived, ministry of health officials hung banners in the streets and sent text messages about handwashing with soap, but to comply, people need clean water.
Insanitary conditions have been the norm for Haiti's poor for a long time. Dramatic improvements are unlikely while people are still living in tented camps.
Haiti's cholera epidemic may last for years. Zimbabwe had a major outbreak in 2008 that is still not over and has spread to neighbouring countries. By the beginning of this year, there had been nearly 99,000 cases and more than 4,000 deaths. (Sarah Boseley is health editor of the Guardian) — © Guardian Newspapers Limited, 2010