"We've just had typhoid cases before the cyclone and that's something we're concerned about," the radio station quoted her as saying.
"We're also concerned about other things, like leptospirosis and diarrhoea, especially that now in the rural areas the water system would be affected in some way."
Tomas packed winds of up to 205 kilometres per hour and gusts of up to 280 kilometres per hour when it first hit Fiji late on Friday.
"[Our] first priority is to carry out an assessment to determine the full extent of the damage... [and] emergency supplies including food and water shall be delivered to the effected regions"
Frank Bainimarama, Fiji prime minister and military chief
Nearly 20,000 people have been living in emergency shelters since Tomas destroyed many villages in northern Fiji.
Only one death was reported so far, while the UN estimates about 150,000 people may have been displaced.
The full extent of the damage has yet to be determined because communications to the hardest-hit areas remain cut off and may not be restored before the weekend.
A nationwide curfew imposed was lifted on Wednesday, but a state of emergency will remain in effect for 30 days in the country's northern and eastern divisions.
Frank Bainimarama, Fiji's prime minister and military chief, said the damage caused by Tomas was "evident" and "overwhelming".
"The government's first priority at this stage is to carry out an assessment to determine the full extent of the damage, while carrying out these assessments emergency supplies including food and water shall be delivered to the effected regions," he said on Thursday.
Power, water, sewage and communications were still disrupted in many northern areas, but a key airport at Labasa in northern Vanua Levu reopened for emergency aid flights.
Troops were deployed to provide relief, including food, water, tents, tarpaulins and basic supplies.
On Thursday Fijian naval vessels and Australian and New Zealand aircraft laden with supplies headed to isolated northern islands that bore the full brunt of the storm.
|Australia and New Zealand have pledged $1.6m in initial emergency funding [AFP]
Australia and New Zealand have also pledged a total of $1.6m as initial contributions to the aid effort.
Inia Seruiratu, the top official for the northern region, told Fiji commercial radio that an aerial inspection of the northern island of Cikobia had revealed widespread damage to vegetation, buildings and infrastructure.
"But overall, the extent of the damage is not as bad as we anticipated, so that is good news," he said.
According to Fiji's weather bureau, Tomas blasted through the northern Lau and Lomaiviti island groups and the northern coast of the second biggest island, Vanua Levu, on Friday before losing strength as it moved out to sea.
Pajiliai Dobui, a senior Fiji disaster management official, said many villages in the northern islands lost more than half their houses in the storm, adding that one village on the island of Taveuni lost all its houses.