Locally transmitted Zika cases: A timeline

There have been 41 cases of locally transmitted Zika virus infections in Singapore, with the transmisson likely to be localised within the Aljunied Crescent-Sims Drive area, say authorities.

Health Minister Gan Kim Yong confirmed on Sunday (Aug 28) that it was the report of the first locally transmitted case that prompted the Ministry of Health (MOH) to look back into past cases “where people were seen by doctors but were not suspected to have Zika”.

In a press briefing, officials from MOH and the National Environment Agency (NEA) said that fresh blood and urine tests conducted on some of these individuals picked up the Zika virus, which can be detected “up to a month” after recovery. Based on these tests, the earliest case of locally transmitted Zika infection is likely to have occurred on Jul 31, according to MOH.

TRANSMISSIBILITY OF ZIKA VIRUS
According to MOH, Zika is a generally a “mild” illness, with four in five people not showing symptoms. For the one in five who develop symptoms, it causes a viral fever with skin rashes, body aches and headache. Mild or asymptomatic cases may still transmit the infection.

Patients are usually not infectious after the fifth day after developing symptoms, as the transmissibility period is between three and five days, said Professor Leo Yee Sin, Senior Consultant of the Communicable Disease Centre (CDC) at Tan Tock Seng Hospital.
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TIMELINE OF EVENTS

• Aug 22: A clinic in the Aljunied area, Sims Drive Medical Clinic, informed MOH of an unusual increase in cases with fever, rash and joint pains. Cases were mild.

• Aug 23: MOH visited the clinic and discussed the cases with the GP. The initial hypothesis was a cluster of mild viral illness transmitted from person to person. MOH then made arrangements for the clinic to refer new cases to the CDC for further testing and to start tracing past cases for review, and testing if appropriate. The ministry also communicated with nearby clinics and construction sites to increase vigilance and report cases to them.

• Aug 25: MOH approached the contractor of a nearby construction site for records of workers with fever. At the same time, a 47-year-old Malaysian woman, who is the first reported locally transmitted case, developed fever, rash, and conjunctivitis.

• Aug 26: The woman, the only female among all 41 cases to date, visited the same GP and was referred to the CDC.

• Aug 27: The woman was confirmed by the CDC to have the Zika virus infection. She was warded. As she was assessed to have been infected in Singapore, NEA was notified and they commenced vector control (anti-mosquito breeding) operations. Members of the woman's household were screened. Tests were conducted on 123 people who were recently or currently symptomatic. This includes 118 construction workers of the nearby construction site. 

• Aug 28: MOH and NEA hold a press briefing during which it is announced that 41 locally transmitted Zika cases have been identified, with 34 patients making a full recovery. The remaining seven are recovering in hospital. The authorities say more cases are likely.