Haitian children clear water from their home after their district of Cité Soleil in Port-au-Prince was flooded by heavy rain from Hurricane Tomas. (Eduardo Munoz/Reuters)

A cholera outbreak has spread into Haiti's capital, where roughly 1.3 million are living in temporary camps and tent cities after January's devastating earthquake.

Health authorities told The Associated Press on Monday that tests confirmed a three-year-old boy who hadn't been out of the city had caught the disease. More than 100 other suspected cholera cases among city residents also were being tested, though officials said some of the others have travelled to other areas in Haiti.

The outbreak has already killed at least 544 people in Haiti, Health Ministry executive director Gabriel Timothee told the AP.

The boy was tested after being taken to the Bernard Mevs/Project Medishare hospital Oct. 31 suffering from severe dehydration, nausea, vomiting and diarrhea. He was treated with oral rehydration, IV fluids and antibiotics and was released.

People walk in a flooded street after Hurricane Tomas passed through the Cité Soleil neighbourhood in Port-au-Prince on Saturday. (Ramon Espinosa/Associated Press)

A stool sample tested by Haiti's national laboratory contained vibrio cholerae 01, the bacteria causing the disease, the chief medical officer, Dr. Antonia Eyssallenne, confirmed to AP in an email.

The boy's family had not travelled in more than a year or had contact with anyone from the Artibonite Valley, where the epidemic was first registered and has wreaked its most ferocious damage.

Timothee said many of the patients hospitalized in the capital with cholera are believed to have recently arrived from the Artibonite Valley, an agricultural area where more than 6,400 of Haiti's known 8,138 cases have been recorded.

At least 114 of the people suspected of having the disease in the capital are in the Cité Soleil slum, the expansive oceanside shantytown at the capital's far northeastern edge and its closest point to the valley.

Since its discovery in late October, the disease has spread to half of Haiti's 10 administrative regions, or departments. More than 200 people have been hospitalized in the West department, where Port-au-Prince is located.

Cholera had never been documented in Haiti before its appearance last month.

In little more than three weeks it is suspected of infecting tens of thousands of people, though only about a quarter of people infected normally develop symptoms of serious diarrhea, vomiting and fever. Nearly four per cent of the thousands hospitalized have died, most from extreme shock brought on by dehydration.

Deteriorating living conditions

Officials are concerned that floods triggered by Hurricane Tomas on Friday and Saturday could exacerbate the spread of the disease, which is transmitted through the consumption of fecal matter contained in contaminated water or food. The release of a dam on the Artibonite River caused the infected waterway to swell Monday, but there were no reports of major flooding.

Living conditions in Port-au-Prince's earthquake camps have "deteriorated as a result of the storm," Boston-based Partners in Health said Monday.

"Standing water, mud, lack of garbage collection and limited sanitation availability make the camps a potential flashpoint for cholera outbreak," the group said.

Humanitarian groups and Haitian health-care workers have been working in Port-au-Prince to prepare for cholera, informing residents about preventative measures such as regular hand-washing and sufficiently cooking food as well as setting up clinics in expectation that the disease would spread to the city.

The origin of the outbreak continues to be a source for debate. Analysis by the U.S. Centers for Disease Control and Prevention has found that the cholera outbreak in Haiti most closely matches a strain of the disease found in South Asia.

Public health experts, including United Nations deputy special envoy to Haiti Paul Farmer, have called for an aggressive investigation into the origin of the outbreak.