Survivors of last month’s quake and tsunami in Indonesia still face the risk of deadly disease outbreaks such as cholera, but epidemics could be controlled, a senior U.N. official said on Tuesday.

Eigil Sorensen, special envoy of the World Health Organisation (WHO) to Indonesia, told Reuters there had been no cases yet of cholera in devastated Aceh province.

He said the number of people likely to die from such deadly diseases would be limited because of a strong monitoring system now in place and due to the initial fast response of the international community and the government to the disaster.

“I think there is still a risk for an outbreak of disease because people are living in temporary conditions which are not really ideal,” Sorensen, the top WHO official in Aceh, said in an interview in the provincial capital Banda Aceh.

“At this stage, I think there is a good system in place. So I think if there is an outbreak of disease like cholera, I think it can be contained. I don’t think there will be any large outbreaks.”

The monster waves of the tsunami destroyed hospitals, medical clinics and forced tens of thousands of people to live in temporary camps in Aceh. Many doctors and nurses were among the more than 228,000 people who are dead or missing.

There had been 91 cases of tetanus mainly related to the tsunami, with 11 deaths, Sorensen said. Diarrhoea cases were being reported every day, while there had been more than 30 cases of measles, which Sorensen said was more of a worry.

Immunisation of hundreds of thousands of children for measles was not going as fast as the WHO would like, he said, adding around 30,000 children had been protected as of last week. The danger with measles was it could spread easily among populations that had not been immunised, he said.

Sorensen said shelter and sanitation for the more than 600,000 homeless in Aceh needed to be improved, but he added that most people had access to some health care one month after the tsunami.

One major concern was the mental health of those in the region, which takes in shattered cities like Banda Aceh and areas along a western coastline that stretches for 350 km (220 miles).

He said there could be up to one million people affected in terms of those who lost relatives, their homes or livelihoods.

Around 5-10 percent could suffer from depression over the long term, he said. That meant it was important to strengthen the capacity of the health sector to deal with such problems.

“Even if you say five percent of the population will have long-term effects, that’s a large number,” Sorensen said.

He said it would take a minimum of two to three years to rebuild Aceh’s health system.

“If you look to the months ahead, the restoration of health services is a critical issue. That means a child is born, it’s attended to by a qualified person and gets normal immunisations,” he said.