A far higher number of babies in Colombia have developed microcephaly related to Zika virus infections than previously reported. The news, reported in the Morbidity and Mortality Weekly Report (MMWR), may help resolve a puzzle: After Brazil, Colombia is the country that has been hardest hit by the mosquito-borne disease, yet it appeared to have far fewer microcephaly cases per capita than its southern neighbor. It now appears that incomplete reporting may explain some of the disparity. Notably, no Colombian institution signed a Zika-inspired pledge last February that banded together many countries (including Brazil), foundations, and journals to “share data at the earliest opportunity.” The U.S. Centers for Disease Control and Prevention (CDC), which publishes MMWR, was a signatory.
The MMWR update, co-authored by scientists from CDC and Colombia’s ministry of health and national institute of health, offers “preliminary information” about 476 cases of microcephaly identified over the last 11 months. In contrast, the latest World Health Organization (WHO) “situation report,” with data current to 7 December, said that Colombia had only reported 60 cases of microcephaly or central nervous system malformations potentially linked to Zika. Brazil had 2211. (WHO reports the numbers given to them by countries, and each country sets its own standard for what qualifies as a case that is “suggestive of” or “potentially associated with” Zika infection.)
Zika is probably not to blame for all of the 476 cases. The paper reports that 306 of the affected babies were tested for Zika virus infection with the ultrasensitive polymerase chain reaction that detects viral RNA or immune markers. Just under half, 147, had evidence of Zika virus infection. Other infections also can cause microcephaly; in fact, out of 121 infants tested for other pathogens, 26 had evidence of infection with either toxoplasmosis, herpes simplex, cytomegalovirus, and syphilis. Seventeen babies were infected with both Zika and another disease known to cause birth defects.
The report does not discuss the discrepancy with WHO numbers. “The majority of cases of microcephaly and other central nervous system defects are still undergoing investigation to determine whether they are linked to Zika virus infection during pregnancy,” a CDC spokesperson told ScienceInsider. He said Colombian health authorities would have to address questions about the timing of their reporting Zika-positive cases of microcephaly to WHO.
ScienceInsider spoke with the lead Colombian spokesperson who said she would reply to the question later today.