Updated
October 2nd, 2019

Mexico Under-Reported Zika Cases

Zika virus CDC travel alerts remain active for Central America and the Caribbean Islands

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According to new reporting, the incidence of Zika virus disease (ZVD) in Mexico was higher than previously assumed. 

This new study estimated that the number of symptomatic cases of Zika infection in the general Mexican population was 7.3 times greater than the corresponding number of reported cases. 

Zika virus is a mosquito-borne flavivirus. The majority of people infected with Zika virus do not develop symptoms. But, Zika virus infection during pregnancy is a cause of microcephaly in the developing fetus, says the World Health Organization.   

This study’s data is based upon the National System of Epidemiological Surveillance. 

Specifically, from January to December 31, 2016, 43,725 suspected cases of ZVD were reported. Of these cases, 5,676 (13%) had a suitable sample for RT-PCR for ZIKV identification. 

Of these cases, 1,700 were positive by RT-PCR for ZIKV, with a mean period of positivity of 0.32. 

These findings in Mexico are similar to those in Colombia, which had 4 percent of cases confirmed in the same year. 

These researchers estimated a total of 13,487 positive cases, which is 30.8% of the suspected cases. 

Which means, the total rate of positive estimated cases was 25.3 per 100,000 among the estimated positive cases 

In total, 78.9 percent of suspected ZVD cases were reported in Mexico’s southeastern region. This geographic trend is related to the lower elevation, where the Zika-spreading Ae. aegypti mosquito is present. 

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For pregnant women who met the operative definition of a suspected ZVD case, samples were obtained from 100 percent of cases. 

A confirmed case of ZVD was defined as a suspected case of ZVD who was positive for ZIKV by detecting viral RNA via real-time RT-PCR in blood serum samples taken within the first five days of clinical onset (fever and/or other symptoms). Molecular detection of ZIKV was performed by real-time RT-PCR uniplex. 

These researchers concluded saying, ‘In 2018, there has been a decrease in the number of suspected Zika cases reported in Mexico. This phenomenon has been observed in all countries of Latin America.’ 

‘It is likely that Zika will return when there is an increase in the susceptible population, as with the dengue fever virus.’ 

To better inform American travelers to Mexico and the Caribbean, the US Centers for Disease Control issued Level 1 Travel Alerts for the Zika virus. 

Additionally, the CDC publishes a world map which was last updated September 2018, that identifies which countries have reported Zika cases. 

In the USA, there were 2,490 pregnant women with Lab Evidence of Zika Virus Infection during 2018. 

The CDC says that because a Zika infection during pregnancy can cause severe birth defects, pregnant women should not travel to the areas where Zika has been identified. 

And, partners of pregnant women and couples considering pregnancy should know the risks to pregnancy and take prevention steps.