A total of 311 people from Thrissur, Paravur in Ernakulam district, and Thodupuzha in Idukki were also under observation.
Meanwhile, the college student, who is this year's first case of NiV in the state, continued to be treated at a ward at the Kalamassery hospital near here.
"A total of 311 people are being closely observed and barring four, all the rest are being looked by health professionals in their homes only. The officials are trying to find out, how many of these 311 had any direct contact with the youth, who has tested positive," said Shailaja.
"The samples of the five (in isolation) have been send to various laboratories and the final result is expected either tomorrow or day after. The preliminary findings of these five, do not point to anything serious, but, we will wait till the final results come," said Shailaja.
It was on Tuesday that the youth tested positive and since then the state Health Department has launched a massive programme to ensure that adequate advisories were issued.
People have been asked not to panic, but seek immediate medical attention if fever develops.
Shailaja said that a central team of professionals were already here and their main objective was to identify the source of the outbreak.
The youth who has been confirmed with the Nipah virus, is from Paravur in Ernakulam district. He was studying in Idukki's Thodupuzha.
Last month he came with 16 other classmates for a student internship in Thrissur and later developed fever. He had tried treatment at two private hospitals in Thrissur.
Shailaja said every precaution were being taken to contain the situation by the health professionals at all three places where he has been.
"Tomorrow Chief Minister Pinarayi Vijayan is arriving here to conduct a full review meeting of the situation. At present things are under control and there need be no reason for panic or worry at all," added the Minister.
Last May, the Nipah (NiV) virus attack took away 12 lives, with 22 positive cases reported from Kozhikode and Malappuram districts, a panic has gripped the state ever since Tuesday after the single case of Nipah was confirmed.
U.V.Jose, the then Kozhikode district collector who has arrived in Kochi is overseeing the arrangements and said the hugely successful Kozhikode model of tackling Nipah was appreciated worldwide and the same thing is being replicated here.
( With inputs from IANS )