Academic journal article Bulletin of the World Health Organization

Prevalence of Asymptomatic Zika Virus Infection: A Systematic review/Prevalence Des Infections a Virus Zika Asymptomatiques: Revue systematique/Prevalencia De la Infeccion Asintomatica del Virus De Zika: Una Revision Sistematica

Academic journal article Bulletin of the World Health Organization

Prevalence of Asymptomatic Zika Virus Infection: A Systematic review/Prevalence Des Infections a Virus Zika Asymptomatiques: Revue systematique/Prevalencia De la Infeccion Asintomatica del Virus De Zika: Una Revision Sistematica

Article excerpt

Introduction

By 25 May 2017, 48 countries and territories in the Americas had confirmed autochthonous, vector-borne transmission of Zika virus disease and 26 had reported confirmed cases of congenital syndrome associated with the infection. (1) Symptoms are often very mild or not present. When symptomatic, the infection may include rash, fever, arthralgia and conjunctivitis. Zika virus infection during pregnancy is a cause of congenital Zika syndrome (2) and it may also be a trigger for Guillain-Barre syndrome. (2,3)

It has been widely reported that approximately 80% of people with Zika virus infection are asymptomatic. This statement is based on a household survey on Yap State in 20074 that has been cited in many publications on Zika virus. Among 557 residents who provided blood samples, 414 had immunoglobulin (Ig) M antibody against Zika virus and 156 of these (38%) reported an illness that met the definition for suspected Zika virus disease. However, 27 (19%) of the 143 residents who had no detectable IgM antibody against Zika virus also reported an illness that met the definition for suspected Zika virus disease. The authors concluded that, among participants who had IgM antibody against Zika virus, a total of 19% (38% minus 19%) had symptoms that were likely due to the Zika virus infection. When adjusted to the total Yap population aged 3 years or older, the authors estimated that 18% of those infected (95% confidence interval, CI: 10-27%) had a clinical illness that was probably attributable to Zika virus. From these data we, and other authors, concluded that 82% of the population infected with Zika virus were asymptomatic.

Lack of signs and symptoms of Zika virus infection does not necessarily imply protection from potential complications, such as microcephaly in babies and Guillain-Barre syndrome in adults. This has implications for surveillance, treatment and research efforts. For example, an analysis was conducted of pregnancies completed between 15 January and 22 September 2016, and recorded in the United States Zika pregnancy registry. (5) Among women with laboratory evidence of Zika virus infection, there was no difference in the prevalence of birth defects in babies born to asymptomatic (16/271, 6%; 95% CI: 4-9%) or symptomatic women (10/167, 6%; 95% CI: 3-11%). Thus, if the asymptomatic pregnant women had not been included in Zika virus surveillance the 16 babies born with birth defects may not have been attributed to Zika virus.

Currently, with the exception of asymptomatic pregnant women, only people with suspected infection (i.e. symptomatic) generally undergo laboratory testing for Zika virus infection as part of national surveillance efforts. (6) Thus, the true prevalence of infection and related complications is likely to be underestimated and biased towards those who seek care or develop a viral disease in response to infection. (7) Knowing the prevalence of asymptomatic Zika virus infection is important for assessing the effectiveness and cost-effectiveness of interventions, including vaccines, to prevent or treat infection. The prevalence is also needed for decision-making about the value of scaling-up surveillance efforts.

The aim of the current review was to estimate the prevalence of asymptomatic Zika virus infection in the general population and in specific population groups from observational epidemiological studies.

Methods

We used systematic review methods, including a meta-analysis. (8,9) We registered the protocol on the International prospective register of systematic reviews (CRD42017059342) (10) and followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis statement for reporting. (11)

Inclusion criteria

We included general or specific population-based studies of participants of all ages and from any country: pregnant women, newborns and infants, children, adults, newborns with congenital abnormalities, and adults with Guillain-Barre syndrome and other neurological diseases. …

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