Ly Huynh Kim Khanh of the city's Pasteur Institute told Tuoi Tre (Youth) newspaper that the institute from Nov. 5-8 tested 25 rats and house mice caught in areas near the house of a 55-year-old man who had tested positive for the virus.
The man and his son were bitten by a rat in early September. The son had been vaccinated against tetanus, Khanh said.
On October 17, the father, who had not been vaccinated, was brought to the city's Tropical Disease Hospital with symptoms of high fever, cough and kidney failure. He is currently recovering.
Nguyen Ngoc Anh Tuan, deputy head of the Pasteur Institute's clinical testing ward, said the institute in recent months had been admitting about 35 patients monthly who had been bitten by rats and wanted tetanus shots.
The infection can also occur through urine, saliva or contact with rodent waste products, Dr Vo Minh Quang, deputy head of the hospital's general planning office, said.
Khanh said local residents should exterminate rats and sterilize areas where rats have entered, and should not touch the animals.
When removing the dead rats, they should not throw them out on the street or in a dustbin, but instead call local health clinics.
All dead rats should be burned and buried to a depth of 0.5-1 metres, he said.
When touching rat traps, they should use gloves and wash their hands with soap later.
Tran Phu Manh Sieu, head of the city's Preventive Health Centre, said the patients infected with the Hantavirus might recover after seven or 10 days of being infected.
Doctors said there was no vaccine against the Hantavirus.
Sieu reassured the public that not all rats carried the virus and that many bites did not result in death.
In Vietnam, cases of hemorrhagic fever with renal syndrome caused by the virus have been reported, Quang said.
The hospital and People's Hospital No.115 had diagnosed two patients with the syndrome in 2009. The patients recovered.
There has never been a diagnosis of Hantavirus pulmonary syndrome in the country, he added.