Mistaken for dengue, Zika cases may be underestimated

New York: Official statistics may underestimate the size of the epidemic caused by Zika virus as some Zika cases may be misreported as dengue, say Brazilian researchers.

The methodologies currently available to the public health system and private labs and hospitals may also produce false positives for dengue in patients with Zika because the two viruses are so similar, said lead researcher Mauricio Lacerda Nogueira from Sao Jose do Rio Preto Medical School (FAMERP) in Sao Paulo, Brazil.

The team performed molecular tests on blood samples from 800 people treated as suspected dengue patients at the emergency facility of Hospital de Base, Sao Jose do Rio Preto's reference hospital, between January and August 2016.

The initial diagnosis, based on clinical symptoms and serological tests, was confirmed in only 400 samples. 

More than 100 of the cases analysed were positive for Zika virus, and the virus that causes chikungunya fever was identified in one of the samples.

"These results suggest the classic division usually made between symptoms -- associating conjunctivitis with Zika and joint pain with chikungunya, for example -- is only for classroom use. In practice, the symptoms can't be separated like that," Nogueira said. 

"It's also practically impossible to distinguish between the three arboviruses with the serological tests currently used on a routine basis by laboratories and emergency services," Nogueira noted.

Although new serological methods capable of distinguishing accurately between Zika and dengue antibodies have been developed, so far they are used only in academic research, he added in the study published in the Journal of Clinical Virology.

The World Health Organisation (WHO) recommends that all cases with an uncertain diagnosis should be treated as dengue because the risk of death from dengue is higher than from Zika and chikungunya.

False-positive results for dengue do not jeopardise treatment of patients but generate unnecessary costs for the health service, according to Nogueira.

"Rest and oral rehydration at home is usually sufficient for people with Zika, except pregnant women," he said. 

"A dengue patient, however, must return to the health service for intravenous rehydration and undergo more complex tests. In particular, platelet levels have to be monitored owing to the risk of hemorrhage," Nogueira said.