Disease condition and impact on patients: By 3 August 2017, about 217 000 cases of ZIKV disease and about 3400 cases of associated congenital syndrome had been reported in Latin America and the Caribbean (1). It has been projected that about 12.3 (0.7–162.3) million cases could be expected in Latin America and the Caribbean every year, which could result in about 64 400 cases of Guillain-Barré syndrome and about 4700 cases of microcephaly (2). Although non-congenital ZIKV disease is not generally fatal, the mortality rate among 602 suspected cases of congenital microcephaly in infants in Brazil during the first week of life was 51 per 1000 live births (3). Does the test meet a medical need? Cases of ZIKV infection have been identified in Africa and Asia since the 1950s, and outbreaks of ZIKV disease were first recognized in the Pacific islands in 2007 and 2013. The 2015–2016 outbreak in the Americas further demonstrated the epidemic potential of ZIKV, with capacity for rapid global spread and birth defects, other adverse pregnancy outcomes and Guillain-Barré syndrome. How the test is used: Diagnosis of ZIKV disease depends on the interval between symptom onset and specimen collection. Serum and/or urine specimens collected within 7 days of symptom onset are tested for the presence of viral RNA by RT-PCR. If the result is negative, specimens are tested for the presence of IgM antibodies, with possible confirmatory testing with neutralization assays. WHO guidance (4) is being updated to incorporate guidance on testing for dengue and chikungunya.

Prevalence: The importance of monitoring and controlling ZIKV transmission globally was underscored when WHO declared ZIKV infection and its associated complications a PHEIC, which changed the emergency response into a long-term programme with a sustained global strategy. To date, 86 countries and territories have reported mosquito-borne ZIKV transmission, and 36 have confirmed ZIKV infection-associated microcephaly and congenital Zika syndrome. Congenital Zika syndrome has been reported in the Americas, the Pacific, South and Southeast Asia and sub-Saharan Africa. Evidence from epidemiological studies and animal models of infection with African and Asian ZIKV strains indicates a risk for maternal–fetal transmission and adverse pregnancy outcomes in all regions with ZIKV transmission. Socioeconomic impact: The prospective economic burden of the neurological sequelae of ZIKV infection in South America and the Caribbean is estimated to be US$ 2.3 (US$ 0–159.3) billion per annum (2). In a separate analysis, it was estimated that an attack rate of 0.3% across the six states of Brazil at greatest risk would result in a total cost exceeding US$ 0.5 billion, an attack rate of 1% would cost more than US $1 billion, and an attack rate of 2% would cost more than US$ 2 billion (3).

WHO guidelines: laboratory testing for Zika virus infection. Interim guidance. 23 March 2016 (4)

Discrimination between ZIKV and DENV infections is critical, as pregnant women with ZIKV infection should be managed for possible adverse outcomes, including fetal microcephaly, while those who test positive for DENV should be managed to reduce their risk for severe morbidity and mortality from acute DENV infection.

The activities that will require resources and budgetary commitment are: purchase of equipment and reagents; training in use of the selected assays; appropriate storage conditions for reagents; collection, transport and storage of clinical specimens in optimal conditions for testing; maintenance of diagnostic equipment; and training of health care providers and public health programme managers in appropriate indications for use of tests and interpretation of results.

Consent is required for collection of a serum or cerebrospinal fluid sample. ZIKV infection may have serious implications in certain populations. For example, given the association with microcephaly and other poor pregnancy outcomes, a positive test is a serious, challenging situation for pregnant women. False- positive results may prompt unnecessary medical interventions or follow-up and exacerbate maternal anxiety, and false negative results may fail to identify high- risk pregnancies or proper diagnosis of congenital Zika syndrome. False-positive results may also incur use of limited public health resources for outbreak response and the economic loss associated with travel deferral if an area is identified as having active autochthonous ZIKV transmission. In addition to issues of clinical management, the absence of laboratory methods for detecting ZIKV infection may leave populations and public health programmes vulnerable to emergence and re-emergence of ZIKV transmission and adverse sequelae of congenital malformations and Guillain-Barré syndrome. Reliable ZIKV diagnostic testing is still very limited, especially in resource-constrained settings. The availability of simple, affordable tests will improve detection of outbreaks, accurate diagnosis and appropriate strategies for prevention, patient care and disease control. Better-resourced settings have greater access to diagnostic tests and to maternal and child health care, including pregnancy and antenatal medical services (with prenatal ultrasound and other mechanisms to monitor pregnancies), thus differentially affecting the management of women with ZIKV infection. All commercially available ZIKV antibody tests for use in a laboratory or at points of care and those in the pipeline should be evaluated systematically for specificity, particularly in populations with a high prevalence of diseases caused by other flaviviruses, especially DENV.