Aid agencies have prevented disease spreading through Indonesia’s tsunami-stricken Aceh, but the threat remained strong, the United Nations said on Friday as doctors reported children dying from pneumonia.

Margareta Wahlstrom, the U.N. special coordinator for the disaster, said efforts to prevent the spread of disease in Aceh, on the northern tip of Sumatra island where almost all Indonesia’s 110,200 deaths occurred, should not be relaxed.

“There are no alarm bells ringing, but we cannot slacken our efforts. The threat is still there,” Wahlstrom told a news conference in Jakarta after returning from Banda Aceh, the provincial capital.

“As long as people live in groups where they haven’t yet got good sanitation and good health access, that will have to be given very top-level attention.”

About 700,000 people were made homeless in Aceh by the Dec. 26 earthquake in the Indian Ocean and ensuing tsunami that has killed more than 162,000 in 13 countries. Thousands of Indonesia’s survivors are now living in makeshift camps.

At a large public hospital in Banda Aceh, Belgian paediatrician Bert Suys, 38, told Reuters he had treated at least 13 children this week suffering from pneumonia after ingesting dirty water either during or after the tsunami.

“We have actually had two children die this Wednesday night and one yesterday of severe pneumonia,” Suys said.

The bottom floor of the hospital was severely damaged in the tsunami, and ruined medical equipment, furniture and beds are stacked around the muddy grounds outside the building.

Suys said he was surprised he had not seen any cases of cholera or dysentery, considering the lack of clean water, and raised concerns about how Indonesia would cope once the foreign medical teams had left.

“I think that once the Australians over here and the Germans and we are gone everything will collapse again. I’m afraid for that,” he said, referring to other foreign medical teams staffing the hospital.

But the comments from Wahlstrom and Suys contrast with an assessment overnight by the UN’s World Health Organisation (WHO), which said the risk of large disease fatalities was fading, particularly the threat from water-borne diseases.

WHO said malaria was a key worry and the agency has started spraying areas in Aceh to kill the growing number of mosquitoes that spread the disease, which was already endemic in the region.

Philip Maher, an emergency specialist with the aid group World Vision in Banda Aceh, said fast relief work could usually slow or stop the spread of most disease.

“After disasters like this there are often predictions that there is going to be a second wave of diseases and in most cases it doesn’t happen. Maybe the reason is because there is a warning flare that goes up, and everyone kicks into action.

“Things are not great, but it’s not like a refugee situation in Africa or something like that.”

Yet Suys and Fauzi Arief, 40, the deputy director of a military hospital in Banda Aceh, did not indicate there had been any increase in the normal number of malaria cases with Arief also backing Suys concerns about a cholera or dysentery outbreak.

“Until now there are no cases of dysentery or cholera or other such diseases. But they are still a significant risk in Banda Aceh ... there is not enough clean water,” Arief told Reuters.

But for one young man who swallowed muddy water, it was too late. As his body lay covered on a trolley in the corridor of the military hospital, his brother pleaded with passersby on Friday for money to pay for his brother to be taken away and buried.