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Temporal associations observed between Zika virus infection, GBS, microcephaly
Researchers reported that the number of Guillain-Barré syndrome cases triggered by Zika virus infection in Salvador peaked 5 to 9 weeks after the onset of acute exanthematous illness, and microcephaly cases peaked 30 to 33 weeks after illness outbreaks, strengthening the association between microcephaly and Zika virus infection during the first trimester of pregnancy.
“Although such temporal associations do not prove causation, their strength and pattern makes a major contribution to the growing body of data supporting the association of [Guillain-Barré syndrome (GBS)] and congenital malformations with previous exposure to Zika virus,” Igor A.D. Paploski, DVM, MSc, veterinarian and public health doctoral candidate at the Federal University of Bahia in Salvador, Brazil, and colleagues wrote. “Estimated time lags provide insight into the high-risk exposure period that might lead to these complications and, consequently, help public health and vector control authorities target control and protection efforts more effectively.”
CDC officials recently confirmed that a causal relationship exists between Zika virus infection during pregnancy and microcephaly and other serious birth defects. Although they have been unable to confirm an association between GBS and Zika virus, a 2015 outbreak of GBS that occurred in the Salvador area, while the region had high rates of Zika virus transmission, indicates there may be a relationship, according to data recently presented at the CDC’s Annual Epidemic Intelligence Service Conference.
Ashley R. Styczynski
“We found that the incidence of GBS was nine to 19 times higher than expected during the outbreak period,” Ashley R. Styczynski, MD, MPH, Epidemic Intelligence Service officer at the CDC, told Infectious Disease News. “Additionally, a majority of the patients with GBS reported an acute illness prior to onset of their neurologic symptoms that was characterized by rash, conjunctivitis, and retro-orbital pain, symptoms commonly associated with Zika virus infections.”
There also has been an increase in the incidence of GBS in Colombia, El Salvador, Suriname and Venezuela, all of which have reported Zika virus outbreaks in 2015, according to Paploski and colleagues. Moreover, there was a 20-fold increase in GBS during a previous Zika outbreak in French Polynesia.
In light of these recent reports, Paploski and colleagues investigated the temporal associations between Zika virus outbreaks and cases of GBS and microcephaly in Salvador. The researchers used data collected by the Centers for Information and Epidemiologic Surveillance of Salvador (CIES) to determine the incidence of acute exanthematous illness (AEI) at 10 public health emergency facilities from Feb. 15, 2015 to May 25, 2015, and three facilities up to Dec. 31, 2015. They also identified patients hospitalized with GBS in 2015 and suspected cases of microcephaly up to March 10, 2016.
Overall, CIES reported 17,503 cases of AEI (5.99 cases per 1,000 persons), 51 GBS hospitalizations (1.74 cases per 100,000 persons) and 367 suspected cases of microcephaly (15.6 cases per 1,000 infants). The number of AEI cases peaked from May 3 to May 9, 2015, with GBS cases climaxing 5 to 9 weeks later from June 7 to July 11. The number of suspected microcephaly cases peaked 30 to 33 weeks after AEI cases peaked, with more than 20 cases reported per week from Nov. 22 to Dec. 12.
“Our results support the link between births of children suspected of having microcephaly and exposure of a pregnant woman to an AEI putatively caused by Zika virus during the first trimester of pregnancy,” Paploski and colleagues wrote. “This link was based on the time-lagged correlation between these two factors and the decrease in incidence of congenital manifestations since mid-December 2015.”
The researchers noted that Zika virus infection during pregnancy also may lead to other congenital malformations, which are being investigated by the Brazilian Ministry of Health.
“Additional individual- and population-level investigations, both clinical and epidemiologic are needed, as are increased resources for surveillance, vector control, and diagnostic capabilities to make definitive connections,” they concluded. “With emerging infectious diseases increasing worldwide, investing in public health surveillance on the city, state, national, and global levels is one of the most cost-effective ways to help address these ongoing and increasing challenges.” – by Stephanie Viguers
References:
Rasmussen SA, et al. N Engl J Med. 2016;doi:10.1056/NEJMsr1604338.
Styczynski AR, et al. Guillain-Barré syndrome outbreak – Bahia State, Brazil, 2015. Presented at: Epidemic Intelligence Service Conference; May 2-5, 2016; Atlanta.
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