The cholera outbreak in central Haiti that so far has killed more than 250 people and infected more than 3,000 is the worst health challenge the country faces since the earthquake in January.
There had been no documented outbreak of the disease in Haiti since 1960.
The US Centers for Disease Control and Prevention (CDC) said after the earthquake that while cholera testing should be carried out, the disease was "extremely unlikely to occur".
So why has the epidemic struck now?
It is not clear if the cause of the outbreak will ever be identified, but health experts agree that for cholera to occur, bad sanitation and hygiene have to coincide with people carrying the Vibrio Cholerae bacterium.
Sanitary conditions were poor in many parts of Haiti even before the earthquake, and Dr Brigitte Vasset from the international humanitarian organisation Medecins Sans Frontieres (MSF) in Paris is reluctant to link the outbreak directly with the quake.
"Central Haiti - where most people have been infected - was not the region most affected by the earthquake," she says.
While many displaced people might have sought refuge in the Artibonite region after the disaster, cholera bacteria could have been present in the Artibonite river or a stagnant water source even before the earthquake, Dr Vasset says.
She also points out that while no cases of cholera have been reported from rural areas, this does not mean that it has been completely absent.
"In many African countries there are sporadic cases during the year, then the weather changes or other conditions change, and all of a sudden there is an outbreak," Dr Vasset says, adding that the disease is difficult to predict.
"I have worked in refugee camps where we expected a cholera outbreak - and it never came," she says.
Sarah Morgan, Senior Health Programme Adviser at aid agency World Vision, agrees that it is possible low-level cholera was present in Haiti all along.
"Surveillance data on cholera in Haiti are not available," she says. However, watery diarrhoea has been common in the country, causing 5% to 16% of the deaths among Haitian children, according to CDC data.
With diarrhoea so prevalent and no stringent monitoring by health authorities and 80% of those with symptoms showing only moderate signs of infection, sporadic cases of cholera might not have registered.
"While there might have been no significant outbreak of cholera, it is possible that there was a background level of the disease," Ms Morgan says.
That cholera has now been picked up so quickly after the outbreak in the Artibonite region is a great success for Haiti's health authorities and international organisations working the country, she adds.
On the rise
Cholera is widespread and on the rise, with three to five million cases worldwide, the World Health Organization says.
More than 100,000 people die from the disease every year, with the majority of cases in Sub-Saharan Africa. Epidemics of Vibrio Cholerae are caused by one of two strains: 01, which has been identified as the cause of the current epidemic in Haiti, and the South-East Asian strain 0139.
It is difficult to get a complete picture of the global spread of the disease, because some countries are reluctant to report cholera for fear of travel sanctions, says Adam Kamradt-Scott from the London School of Hygiene and Tropical Medicine.
Mr Kamradt-Scott points out that around 75% of people infected with Vibrio Cholerae do not develop symptoms. But they excrete the bacterium with their faeces for up to 14 days - a potential source of infection for others.
With more people and aid coming to Haiti since the earthquake in January, there is a possibility that the bacterium was brought to the country from the outside, Mr Kamradt-Scott says.
"The bacteria can be resident in water for a quite a while," Mr Kamradt-Scott explains and points to a cholera outbreak in Peru in 1991.
There was speculation that that epidemic, which quickly spread across Latin America, came from bilge water and algae dumped by an Asian cargo ship, contaminating local shellfish.
In Haiti, the disease has more likely been spread because people used the Artibonite river for washing and drinking.
"As soon as people have been infected and excrete the bacteria, the epidemic spreads very quickly," Mr Kamradt-Scott says.
"It is then important to break the cycle of the disease," he adds.
Because Vibrio Cholerae produces toxins that lead to watery diarrhoea, patients need to be rehydrated with liquids containing sugar and salt or with intravenous fluids.
Those infected need to receive treatment immediately, Mr Kamradt-Scott says. If not treated, the death-rate of cholera can rise up to 50%.
But the potentially deadly cholera cycle can only be broken when people also stay away from the contaminated water source until the bacteria have cleared, he adds.