The Health Ministry is advising people returning home from countries with Zika virus infection cases to take screening tests to ensure they are free of the virus.

Health Minister Datuk Seri S. Subramaniam said the precautionary measure was necessary as about 80 percent of those infected by the Zika virus did not show any symptoms, making it difficult to detect the infection.

He also urged Malaysians, especially those in Johor who commute to Singapore daily, to take the blood tests every day.

"There are about 150,000 to 200,000 people who commute from Johor to the city-state every day, this increases the risk of the virus spreading to Malaysia.

"I hope they come forward voluntarily to take the screening tests at all the 12 hospitals in Johor where there are facilities to run the tests to ensure that they are not infected by the Zika virus," he told a press conference here Monday.

Dr Subramaniam said this following the increase in Zika cases reported in Singapore which has now reached 41 locally transmitted cases.

He said symptoms of Zika virus infection could be detected from several days to two weeks.

He also urged anyone with signs of viral infection such as fever, rashes, joint pains and conjunctivitis, to get treatment at the nearest clinic or hospital.

Dr Subramaniam also advised pregnant women or those planning to have children to take blood tests to ensure they were free of the virus which can also spread through sexual intercourse.

He also urged Malaysian supporters to the recent Olympic Games in Rio De Janeiro to come forward voluntarily to take the screening tests by contacting the Zika Operations Room hotline at the National Crisis Preparedness Response Centre (CPRC) at telephone number 03-88810200/700.

He added that the ministry had also conducted tests on all athletes and officials of the national contingent to the Rio Olympics.

"Results of the screening from 56 blood tests and urine tests on those people who returned from Rio de Janeiro found that no athlete or contingent member had been infected by the Zika virus so far," he said.

Dr Subramaniam said the ministry was also monitoring Zika virus infection through continuous laboratory surveillance by the National Public Health Laboratory and the Institute of Medical Research where between June 2015 until last Friday, 784 blood samples had been tested from patients displaying signs of Zika virus infection.

"So far, the results of all the tests have been negative," he said.

Dr Subramaniam also said the ministry had intensified monitoring at all international entry points in the country and distributed pamphlets on the prevention of Zika infection.