Doctors have said there is no need to press alarm buttons after the number of patients testing positive for swine flu reached 51 on Wednesday.
Numbers have gone up because more people are getting themselves tested for the virus, said doctors. Even those without flu-like symptoms could test positive.
"These are sub-clinical cases where the immune system is fighting the virus even as it harbours it," said Dr Pradip Awate, state epidemiologist, Directorate of Health Services.
Several patients are getting tested at a private laboratory in the city instead of opting for free tests run at government or civic-run laboratories, according to the civic administration's figures.
Doctors added that the private lab does not follow protocols laid down by the government for testing swine flu cases.
Since January, 126 were tested at the state-run Haffkine Institute, Parel and Kasturba Hospital, Byculla of whom eight tested positive. During the same period, 323 got tested at the private lab; 43 tested positive.
A swine flu test could cost up to Rs5,000 at a private laboratory, which tests for the virus with a throat swab.
"If people want to pay for getting themselves tested, we cannot stop them. We only test high-risk patients such as children, pregnant women, diabetic or high blood pressure patients among others or patients admitted with complications," said Dr Mangala Gomare, epidemiologist, Brihanmumbai Municipal Corporation (BMC).
If someone in the family is tested with H1N1 virus, the others in the family need not be tested for it, unless they fall under the high-risk category. "People who have flu-like symptoms need not test for the virus and could start treatment with Tamiflu," said Dr Abhay Choudhary, director of Haffkine Institute.