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Maternal-fetal transmission and adverse perinatal outcomes in pregnant women infected with Zika virus: prospective cohort study in French Guiana

BMJ 2018; 363 doi: https://doi.org/10.1136/bmj.k4431 (Published 31 October 2018) Cite this as: BMJ 2018;363:k4431

Re: Adverse perinatal outcomes in pregnant women infected with Zika virus in French Guiana: missing confounders?

Sir,

I read with interest the recent article by Pomar et al. which indicates the incidence of Zika virus (ZIKV) related congenital disease in French Guiana was lower than that reported elsewhere in the early days of the South American ZIKV epidemic[1].

I am curious to know about some possible potential confounding factors apparently not mentioned in this paper. I note that although alcohol consumption states was reported, tobacco smoking/use was not, even though smoking is well-known to have deleterious effects on pregnancy e.g. intra-uterine growth retardation (IUGR)[2]. Did the authors list alcohol consumption but not tobacco smoking because the former is a prevalent habit in the French Guianan pregnant population but not the latter? It would be helpful to understand why this important risk factor for adverse pregnancy outcomes was not presented along with alcohol consumption.

The other potential confounding factor which could affect pregnancy & fetal outcomes is consanguinity. I have never been to French Guiana and am not familiar with it is demographics. However, I note the Centre Hospitalier de l'Ouest Guianais (CHOG) is in Saint Laurent du Maroni. I understand this is near the Maroni River area of French Guiana. I have gleaned from a quick search of the literature that the Maroni River area is populated by descendants of escaped African slaves, a people known as Maroons. The Maroons are apparently quite a genetically distinctive population with little mixing with French Guiana's other ethnic groups. This has led to a relatively high incidence of some genetic diseases like Infantile Pompe's Disease in this population[3].

Although Pomar et al comment on the socio-economic challenges facing the Maroni River population, they do not mention consanguinity or the limited genetic diversity of this population, which could affect the rates of congenital anomalies. It would be interesting to hear the CHOG group's opinion on this point as they undoubtedly have the local expertise to make a more informed commentary on this than I can.

Without further information on these important confounding factors, it is difficult to dispel a "Devil's Advocate" suspicion that the observed adverse fetal outcomes attributed to congenital Zika syndrome (CZS) are due in part to factors other than CZS in the distinctive Maroni River population.

References:
[1] Maternal fetal transmission and adverse perinatal outcomes in pregnant women infected with Zika virus: prospective cohort study in French Guiana. Pomar L et al. BMJ 2018';363k4431 https://www.bmj.com/content/363/bmj.k4431
[2] Smoking and pregnancy - A review on the first major environmental risk factor of the unborn. Mund M et al. Int J Environ Res Public Health 2013 Dec; 10(12):6485-6499 https://dx.doi.org/10.3390%2Fijerph10126485
[3] Incidence of Infantile Pompe Disease in the Maroon population of French Guiana. Elenga N et al. BMJ Paediatrics Open 2017; 2(1) http://dx.doi.org/10.1136/bmjpo-2017-000182

Competing interests: No competing interests

26 November 2018
Gee Yen Shin
Consultant Virologist
University College London Hospital NHS Foundation trust
250 Euston Road, London, NW1 2PG