Incidence of SARS-CoV-2 infection is difficult to estimate in newborns due to difficulty in determining the timing of the occurrence. Although some evidence may be favorable to the existence of vertical transmission, a first positive test in the newborn can mean viral replication or just contamination during passage through the vaginal canal or from the environment.1 The World Health Organization has issued recommendations on the diagnosis of intrauterine Sars-CoV-2 infection which is based on the following three key conditions: evidence of maternal infection during pregnancy, in utero fetal Sars-CoV-2 exposure (positive placental or <24h of life newborn RT-PCR or newborn IgM/IgA), and confirmation of viral persistence or immune response in the neonate (positive RT-PCR in a newborn´s sterile sample at 24-48h of life).2 Upper respiratory tract secretions are not sterile. In our experience, with 94 deliveries of pregnant women who had SARS-CoV-2 during pregnancy, between February 2020 to February 2021, we found 2 newborns with a 1st positive test (SARS-CoV-2 RT-PCR from upper airway sample, collected <24h of life), but with 2nd negative result collected between 24-48h of life (upper respiratory tract RT-PCR and serology). Both newborns were asymptomatic suggestive of false positives, probably due to contamination during vaginal canal. It is recommended to bathe newborns after birth to try to remove virus remains which can be present in newborn nose or skin surface.3 Although breastfeeding was initially contraindicated in mothers with SARS-CoV-2 infection, with the evolution of knowledge, we already know that it is possible for a mother to breastfeed and share the same room, as long as the mother maintains hygiene measures and use of a mask because transmission is more likely from respiratory secretions and less likely from breast milk.3 The testing time is not consensual and there are differences in the recommendations between societies. Center for Disease Control and Prevention4 regardless of the presence of maternal symptoms suggest doing a SARS-CoV-2 test at 24 hours of life with repetition at 48h of life, if the first test is negative, similar to American Academy of Pediatrics (AAP).3 In contrast the Spanish Society of Neonatology proposes the hypothesis of testing before 24h of life and after 48h.5 In case the newborn first test is positive it is recommended to obtain a new test, between 24-48h of life, and serologies (IgM) to confirm the vertical infection or, in case of both negative, confirm that it is a false positive.
Thus, one should be aware of false positive SARS-CoV-2 RT PCR in newborns born to infected mothers and further testing with repeat PCR and serology at 48 hours is recommended.
André Coelho Almeida1, Maria João Vieira2.
