Evidence of possible vertical SARS-CoV-2 transmission according to the World Health Organization criteria in asymptomatic pregnant women.

OBJECTIVE: SARS-CoV-2 vertical transmission has been extensively investigated. Recently, the World Health Organization (WHO) published strict criteria to classify the timing of mother-to-child transmission into different categories. The aim of this study was to investigate the possibility of vertical transmission in asymptomatic SARS-CoV-2 positive women. METHODS: We included 42 pregnant women fulfilling the inclusion criteria which presented a positive nasopharyngeal test at 24-48 hours before delivery and had obstetric indication of cesarean section at a Perinatology center in Mexico City. All women were asymptomatic at the time of the test. The newborns had both oral and rectal swabs collected at birth and at 24 hours after birth. Viral detection was carried out by RT-PCR in all samples. Relevant medical information was retrieved from clinical records. RESULTS: Initially all women were asymptomatic for COVID-19 and 25 (59%) developed mild disease after discharge. Three (7%) neonatal deaths occurred, none of them had a positive SARS-coV-2 test nor COVID-19-related symptoms. There were five cases of intrauterine transmission of SARS-CoV-2, according to the WHO criteria. Our results also showed that performing only one neonatal swab (oral or rectal) may reduce SARS-CoV-2 detection by 40%. CONCLUSION: This study contributes with evidence to reinforce the existence of vertical transmission even in asymptomatic patients and highlights the importance of testing more than one sample in newborns to increase the detection rate of SARS-CoV-2. This article is protected by copyright. All rights reserved.