New Delhi: If one comes across a patient infected with the deadly nipah virus, keeping a metre's distance is important, virologists say.

The nipah virus spreads not through the air but through droplets secreted by the patients.

"Droplets don't travel beyond a metre. One of the key criteria for infection control is to stay at least one metre away from the patient," said G. Arunkumar, head of the Manipal Centre for Virus Research in Karnataka.

The Union health ministry said on Thursday that 14 patients had been "confirmed" with nipah infection in Kerala and that 12 of them had died.

Some 20 "suspected cases" are under treatment and observation in medical college hospitals in Kozhikode and Thiruvananthapuram.

A central team from the New Delhi-based National Centre for Disease Control that had flown into Kerala on May 21 said on Thursday that the nipah infections were "not a major outbreak but a local occurrence".

Health officials say it's not clear yet how the virus had slipped into the "index case" or first patient during the current outbreak. They say that all the other nipah-infected patients in Kozhikode and Malappuram had contact with the index case or other patients.

Scientists had isolated the nipah virus in 1999 after an outbreak in pigs and humans in Malaysia and Singapore. The virus caused multiple outbreaks in Bangladesh between 2000 and 2013 and two in India -- in Siliguri (2001) and Nadia (2007) districts of Bengal - before the latest outbreak in Kerala.

Fruit bats are the natural reservoirs of the nipah virus. In Bangladesh, the outbreaks were attributed to the consumption of date palm sap contaminated with fruit bat saliva or urine that contained the virus.

India's health ministry has issued advisories asking people in "high-risk areas" not to consume unwashed fruits or fruits half-eaten by birds or animals, and to avoid entering abandoned wells. "Bat secretions laden with (nipah) virus can infect people during fruit tree climbing, eating or handling contaminated fallen fruits or consuming raw date palm sap or toddy."

Human-to-human infection can occur from close contact with people infected with the nipah virus at home or in hospitals if appropriate personal protective equipment is not used, the advisory said.

It called for a modification of the traditional rituals and practices while disposing of the bodies of people suspected to have died of nipah infections so that family members are not exposed to the disease.

The illness commonly presents as brain inflammation but in some patients, the early phase of the illness may also be marked by fever, persistent cough and difficulty in breathing.