Patients with ZVD
From August 9, 2015, through April 2, 2016, a total of 65,726 cases of ZVD were reported in Colombia, with 2485 (4%) that were positive on RT-PCR assay. During this period, 11,944 pregnant women with ZVD were reported in Colombia, with positive results on RT-PCR in 1484 cases (12%). There is currently complete information on gestational age at the time of symptom onset for a subgroup of 1850 pregnant women with ZVD.
Cases are shown according to the week of the onset of symptoms.
Among the 65,726 patients who were reported to have ZVD, 2336 (4%) were hospitalized at the time that the case was reported, including 938 of the 11,944 pregnant women (8%). The number of reported ZVD cases steadily increased from October 2015 through January 2016, with the largest number of cases reported during the week of January 31 to February 6 (epidemiologic week 5) (Figure 1). From February 7 to April 2 (weeks 6 to 13), the number of reported cases decreased overall, although a few areas were reporting an increased number of cases at week 13.
Extent of ZVD Outbreak
Shown are the reporting areas, which include 32 departments (i.e., states) and 5 districts (the major cities of Barranquilla, Bogotá, Buenaventura, Cartagena, and Santa Marta). The total incidence of Zika virus disease was reported separately for Barranquilla (which had 348 cases per 100,000 population), Cartagena (88 cases per 100,000), and Santa Marta (376 cases per 100,000). The Instituto Nacional de Salud did not report the incidence in Bogotá, since the cases originated in other reporting areas. The incidence in Buenaventura was included in the total number for the state of Valle del Cauca.
Shown is the incidence of Zika virus disease among pregnant women per 100,000 women of childbearing age in the reporting areas described in Figure 2. The incidence in these women was reported separately for Barranquilla (which had 342 cases per 100,000), Cartagena (27 cases per 100,000), and Santa Marta (306 cases per 100,000).
Zika virus has spread rapidly throughout Colombia since the first locally acquired case was confirmed. The ZVD cases are widely distributed across Colombia, with at least one laboratory-confirmed case in 35 of the 37 reporting areas. Seventeen reporting areas had more than 1000 cases; 59,585 cases (91%) were reported from these 17 areas (Figure 2). The highest incidence of ZVD (1342 per 100,000 population) was reported on San Andres and Providencia, islands in the Caribbean Sea, which was followed by an incidence of 655 per 100,000 in Norte de Santander, a state in the northeast region of the country adjacent to the Venezuelan border, and an incidence of 517 per 100,000 in the state of Huila. For pregnant women, the highest incidence of ZVD was reported in Norte de Santander (621 per 100,000 women of childbearing age), the city of Barranquilla (342 per 100,000), and the state of Huila (333 per 100,000) (Figure 3). Similar geographic patterns were seen for laboratory-confirmed cases.
Shown are data for 582 pregnant women with symptoms of Zika virus disease for whom Zika virus RNA was detectable on reverse-transcriptase–polymerase-chain-reaction (RT-PCR) assay. Of the 582 samples, 326 (56%) were positive for Zika virus. The mean number of days from the reported onset of symptoms to sample collection was 2.6 days for RT-PCR–positive samples and 4.0 days for RT-PCR–negative samples.
Of the 3384 Zika RT-PCR assays that were performed in Colombia during this time period, 2037 (60%) were conducted on samples obtained from pregnant women; 73% of the samples obtained both from the total population and from pregnant women had positive results. Among a subgroup of 1850 pregnant women with complete data, 582 had serum samples tested on RT-PCR assay; of these samples, 326 (56%) were positive for Zika virus (Figure 4). Among samples that tested positive on RT-PCR assay, the mean number of days from the reported onset of symptoms to sample collection was 2.6 (median, 2.0; range, 0 to 21). For samples that were RT-PCR–negative, the mean number of days from the reported onset of symptoms to sample collection was 4.0 (median, 2.0; range, 0 to 76)
. Among the RT-PCR–positive samples, 10 of 326 (3%) were collected more than 7 days after symptom onset; among RT-PCR–negative samples, 17 of 256 (7%) were collected more than 7 days after symptom onset. Among all 555 samples that were collected up to 7 days after reported symptom onset, 316 (57%) were positive on RT-PCR assay. Among the RT-PCR–negative samples, 8 had positive results for dengue and 23 had positive results for chikungunya.
Female-to-Male Incidence Ratio
Two thirds of the reported ZVD cases were diagnosed in female patients, although these results were probably affected by referral and testing bias because of the concern about ZVD during pregnancy. There was significant variation in estimated incidence according to sex and age (Table 1). Although the incidence of ZVD was similar in girls and boys who were 4 years of age or younger, the incidence was significantly higher among female patients than among male patients in all other age groups. The incidence of ZVD was approximately three times as high among girls and women between the ages of 15 and 29 years as among boys and men in the same age group. The highest incidence ratio comparing female patients to male patients was 3.42 (95% confidence interval [CI], 3.25 to 3.59) among those between the ages of 20 and 24 years. The incidence ratios between female patients and male patients were larger when the analyses were limited to laboratory-confirmed cases.
Data on Trimester of Infection
At the time of this report, most pregnancies with ZVD were still ongoing, and key data, including the trimester in which ZVD was diagnosed, are still being collected. Among a subgroup of 1850 pregnant women with ZVD for whom complete data on the trimester of infection were available, 532 reportedly contracted the infection in the first trimester, 702 in the second trimester, and 616 in the third trimester. At the time of data cutoff, among the women in whom ZVD had been diagnosed, pregnancies were ongoing in 84% of those with a diagnosis in the first trimester and in 71% of those with a diagnosis in the second trimester. For the 616 women in whom ZVD was diagnosed in the third trimester, 82% of their infants were born at term with a normal birth weight, 2% were born at term with a low birth weight, 8% were preterm, and 1% died during the perinatal period; 7% are still being followed. No cases of microcephaly or brain abnormalities have been reported in this group to date.
National Surveillance for Microcephaly
From January 1, 2016, to April 28, 2016, a total of 50 infants with possible microcephaly were reported to the national surveillance system for birth defects. Of these cases, 26 are still under investigation, and 20 were deemed to have resulted from causes other than Zika virus infection, including STORCH (syphilis, toxoplasmosis, other agents, rubella, cytomegalovirus, and herpes) infections, genetic causes, neural-tube defects, and other causes among infants with negative results on Zika RT-PCR whose mothers had no symptoms of ZVD during pregnancy. Four infants with microcephaly had laboratory evidence of congenital Zika virus infection on RT-PCR assay, a negative STORCH evaluation, and normal karyotypes. Of the 4 infants, who were born between 37 and 39 weeks of gestation, 1 had abnormal brain findings on ultrasonography and 3 had abnormal findings on hearing evaluations. Other clinical findings for the cases included decreased muscle tone, problems sucking or swallowing, and amyoplasia of the lower limbs. None of the four mothers had symptoms of ZVD during pregnancy and therefore were not reported as part of ZVD monitoring.