Zika-Associated Microcephaly Epidemic and Birth Rate Reduction in Brazilian Cities

Abstract

Objectives. To estimate birth reduction potentially in response to Zika virus–associated microcephaly among the 36 largest Brazilian cities.

Methods. We analyzed the number of live births per month on the basis of information on approximately 8.2 million births from all of Brazil’s state capitals and cities that had more than 10 000 annual births.

Results. In the second half of 2016, the live birth rate was reduced by 7.78% (95% confidence interval [CI] = 6.64%, 8.89%; P < .001). This reduction was correlated with the Zika virus–associated microcephaly rate. In the cities with the highest microcephaly rate in 2015 (> 1 case per 1000 live births), the reduction in the live birth rate was 10.84% (95% CI = 8.58%, 13.04%).

Conclusions. The birth rate in the largest Brazilian cities during the second half of 2016 was significantly reduced, which is potentially the effect of a birth control recommendation prompted by an epidemiological alert.

Public Health Implications. The effects of population-based interventions should be weighed by considering the actual risk of disease and the sociodemographic impact of strategies such as birth control.

Zika virus (ZIKV) was recently introduced to Latin America, most likely from the Pacific Islands, causing a large epidemic.^1,2 By September 2015, an increasing number of infants with microcephaly were noted in Brazil’s northeast.² Subsequently, these cases were associated with ZIKV infection.^2–4 On November 11, 2015, the Brazilian Ministry of Health declared microcephaly a national public health emergency.⁵ Concurrently, there were frequent media reports of recommendations for couples living in ZIKV-affected areas to postpone pregnancy plans.^5,6

The impact of the overall panic on the birth rate has not yet been quantified. However, recent observations suggest a reduction in the birth rate in some Brazilian cities.^7,8 This reduction appears to be significant for the second half of 2016, that is, approximately 9 months after the start of the Zika media coverage.

The population’s reaction to the Zika epidemic may have reduced the number of cases of microcephaly but with the social cost of reducing the birth rate. We estimated the birth reduction potentially associated with the alert of ZIKV-associated microcephaly among the largest Brazilian cities.

METHODS

We obtained information on approximately 8.2 million births from 36 cities (including 27 capitals). We analyzed total live births per month of all the state capitals of Brazil plus cities that had more than 10 000 births in 2015. We restricted our analysis to these cities to avoid bias owing to delays in the notification of births, which are more frequent in smaller cities. We obtained data from the Information System on Live Births (Sistema de Informação sobre Nascidos Vivos) of the Brazilian Ministry of Health (last updated May 3, 2017). We obtained data on ZIKV-associated microcephaly from the Brazilian National Information System for Notifiable Diseases (Sistema de Informação de Agravos de Notificacão).

Using a negative binomial regression model and birth data from January 2007 to June 2016, we estimated the expected number of births for the second half of 2016 for each city. In addition, for each of the cities, we estimated the ratio of the birth rate in the second half of 2016 to the birth rate in the previous periods, adjusted for year and month. We evaluated the correlation between the regression coefficients obtained in these models and the previous incidences of ZIKV-associated microcephaly reported in 2015 for the corresponding cities. We conducted the statistical analyses using Stata version 11.0 (StataCorp LP, College Station, TX).

RESULTS

The number of births from the 36 Brazilian cities grew progressively from 2007 to 2015, from 803 017 to 850 348. However, in 2016 the number of births decreased to 797 564.

The expected number of births for the second half of 2016 in the cities analyzed was 409 773 births. However, the observed number of births for that period was 373 136 births. This reduction was evident starting in July and remained consistent through the rest of the year (Figure 1). In a multiple model adjusted for year, month, and city, the second half of 2016 was associated with a 7.78% reduction in birth rate (95% confidence interval [CI] = 6.64%, 8.89%; P < .001).

FIGURE 1—

Sum of Predicted and Observed Births by Year and Month: 36 Brazilian Cities, 2013–2016

The city-specific analysis showed that 28 of the 36 cities had a statistically significant reduction in birth rate (Figure 2). In 16 of the cities, there were no cases of ZIKV-associated microcephaly in 2015. However, these same cities showed an overall reduction in the birth rate of 6.12% (95% CI = 4.35%, 7.86%). Conversely, in the 13 cities with ZIKV-associated microcephaly cases but with a rate lower than 1 case per 1000 live births, in the second half of 2016, the live birth rate was reduced by 7.99% (95% CI = 6.29%, 9.65%).

FIGURE 2—

Ratio of Birth Rates: 36 Brazilian Cities, Second Half of 2016

Note. Shown is the association between the second half of 2016 and the birth rate in 36 Brazilian cities. The cities are ranked in 3 groups according to the incidence of ZIKV-associated microcephaly reported in 2015. At the top of the figure are the cities that did not have cases (sorted from highest to lowest number of births in 2015). In the second group are the cities that had cases of ZIKV-associated microcephaly but with a rate lower than 1 case per 1000 live births. In the bottom are the cities with a microcephaly incidence higher than 1 case per 1000 live births in 2015. ZIKV-associated microcephaly rates (per 1000 live births) are presented in parentheses.

Finally, in the 7 cities with the highest microcephaly rate in 2015 (> 1 case per 1000 live births), we observed a reduction of 10.84% ​​(95% CI = 8.58%, 13.04%) in the live birth rate during the second half of 2016 (Figure 2). These 7 cities had exhibited a pooled microcephaly incidence of 2.12 cases per 1000 live births in 2015. This suggests that it would be necessary to postpone on average about 471 births to avoid a case of microcephaly. Thus, the observed reduction of births—6901 fewer than expected—has the potential to prevent about 15 cases of microcephaly among this last group of cities.

The adjusted coefficients of the regressions of the live birth rate on the second half of 2016 were negatively correlated with the ZIKV-associated microcephaly rate reported in 2015 (Spearman ρ = −0.38; P = .02).

DISCUSSION

We found a significant reduction in the birth rate of the largest Brazilian cities during the second half of 2016. We found that 28 of the 36 major cities had a statistically significant reduction in the birth rate during the period. Although there could be a concurrent effect of a few other factors, such as the current economic crisis that started in 2014, it is noteworthy that a sharp reduction started approximately 9 months from the beginning of the epidemic.

This association would be expected to be accompanied by growing access to contraception, but a recent study suggested that there was no increase in sales of contraceptives since the ZIKV outbreak in Brazil.⁹ However, we did not analyze nonhormonal methods such as condoms. It is therefore still unclear which strategies the population prefers for birth control in the face of this alert.

Limitations

As a potential limitation of this study, we recognize that there may be delays in reporting live births. However, this risk is minimized by our focus on large cities, where the reporting system is electronic and therefore quickly updated. Additionally, the fact that the ZIKV-associated microcephaly rate was associated with the regression coefficients supports the idea that fear of microcephaly could plausibly be a cause of the birth reduction in the second half of 2016. Consistent with these findings, reports in the media suggest that a widespread fear of microcephaly affected the decision of many couples to have children.⁸

Public Health Implications

Pregnancy postponement may be one of the strategies to prevent congenital disease during a ZIKV outbreak.¹⁰ We estimated the potential impact of birth control recommendation because of the epidemiological alert. However, this impact would only be noticeable in cities with a high incidence of the infection, as in our estimation that birth control could prevent about 15 cases of microcephaly among the 7 most affected cities.

Although the epidemiological alert was restricted to affected areas, its effect on family planning and on the country’s demographic structure is worrying. It is noteworthy that the reduction occurred even in cities with few or no cases of ZIKV-associated microcephaly. For this reason, in some populations the recommendation to postpone pregnancies may be weakly justified. In this sense, risk communication must be carefully conducted during public health emergencies, and journalism must be a partner in this process, which must be contextualized and communicated cautiously.

The acute and long-term threat to pregnant patients is not over because large geographic areas still contain susceptible populations.¹¹ Whether Zika will continue to be an intermittent risk in endemic areas is uncertain.¹² However, population-based intervention effects should be weighed by taking into account the actual risk of disease and the sociodemographic impact of strategies such as birth control.