The mainstream media reported a new “cluster” of Zika cases in Singapore yesterday. This involved a couple living in Hougang who almost certainly were infected by local mosquitoes. NEA/MOH were notified on 27th March and a helpful map of the cluster is provided on the NEA website.

Zika clusters in Singapore – screenshot from the NEA website from this morning.

In general, perhaps because the clinical disease is mild (and up to 80% of those infected are asymptomatic) and testing is infrequent, the number of reported cases of Zika has been very low following the large outbreak in August/September last year. But the recent cases highlight that the virus is still circulating around in Singapore.

By now, there is little dispute that the Zika virus can cause congenital malformations (notably microcephaly) in the newborn of infected pregnant women, particularly if the infection occurred during the first trimester of pregnancy. It is also strongly associated with post-infective neurological sequelae such as the Guillain-Barré syndrome (GBS). The only question is what is the actual risk of each.

Most of the data (and subsequent hype/fear) for congenital malformations are from a small area of northeastern Brazil – Bahia. But the rates of the Zika congenital syndrome have been far higher here than anywhere else in the world, leading to questions about what was really happening over there. The latest publication – a letter in NEJM by authors from the Brazilian Ministry of Health, PAHO, WHO and the research institute Oswaldo Cruz Foundation – showed that despite having a resurgence of Zika in 2016, with a corresponding rise in GBS cases, there was no similar rise in microcrephaly cases despite the heightened surveillance.

Figure from the NEJM article showing no rise in microcephalic cases in Brazil despite the surge in Zika infections.

Obviously this is just a “helicopter-view” epidemiological observation and what’s happening on the ground is uncertain, but it does support the theory that the congenital Zika syndrome is not as common as previously thought. It is certainly far, far below the previous upper projection of 13.2% (of infected pregnant women). None of the (admittedly few) known infected pregnant women in Singapore have delivered babies with congenital malformations, to public knowledge.

The risk is real, just like with cytomegalovirus, rubella or any of the other TORCH pathogens, but there should not be any excess panic or anxiety with this latest “cluster” of Zika cases.