Infection by Chlamydia trachomatis is an important public health problem worldwide, and C. trachomatis is the most frequent bacterial cause of sexually transmitted diseases. The infection can be acquired by passage through the birth canal and may cause neonatal nasopharyngitis and/or conjunctivitis (usually with onset 5–12 days post birth) and pneumonia in the first 3 months of life.1,2 The aetiological diagnosis of these infections is important, as the symptoms overlap with those caused by other microorganisms and treatments that do not include a macrolide may not be effective against C. trachomatis. The aim of our study was to establish the rate of perinatal transmission of infection by C. trachomatis.

We conducted a prospective study between October 2010 and September 2015 by performance of real-time nucleic acid amplification tests (NAATs) (Cobas® 4800 CT/NG, Roche) to assess for the presence of C. trachomatis in 103 newborns of infected mothers identified by screening during the puerperium period at the Hospital Universitario Donostia (HUD).3 The research project was approved by the Ethics Committee of the HUD (memorandum 9/2010). All the participants, as is done routinely in all newborns delivered at the HUD, received ocular prophylaxis with a topical cream (active ingredient: tobramycin through October 2013, and chlortetracycline hydrochloride thereafter). We assessed newborns for vertical transmission 7–10 days post birth by means of a physical examination and collection of a throat swab specimen, supplemented with an eye swab specimen in cases where conjunctivitis was suspected and routinely in the last year under study. Infected newborns received an oral course of erythromycin for 14 days while this formulation was available in hospital, and thereafter a 3-day course of azithromycin. They remained in follow-up for 3 months (parents were directed to seek care if the child developed symptoms of conjunctivitis, pneumonia or nasopharyngitis), and we contacted the family by phone at the end of the follow-up period to confirm the absence of symptoms.

We found evidence of vertical transmission in 11 newborns (10.7%; 5 male and 6 female), with the cases distributed uniformly throughout the period under study. This percentage rose to 15.5% (11/71) if we excluded newborns delivered by caesarean section and/or born to mothers that had received antibiotherapy in the 48h prior to delivery (Table 1). C. trachomatis was detected in 8.7% (9/103) of pharyngeal samples and 17.6% (6/34) of eye samples (P=.15). Seven of the infected newborns were asymptomatic, while 4 (3.9% of the total included in the follow-up) had conjunctivitis, in one case associated with cold symptoms. All infected newborns received antibiotherapy (7 erythromycin, 4 azithromycin), with early resolution of infection observed in 7 out of the 8 that attended the appointment scheduled for microbiological follow-up 15 days later; in another patient, the cultures remained positive for C. trachomatis and the symptoms (conjunctivitis) persisted for 2 months due to poor adherence to treatment by the parents.

The data on the rate of vertical transmission of C. trachomatis is scarce for Europe and non-existent for Spain. In Germany, a study that used culture for diagnosis and excluded newborns delivered by caesarean section or born to mothers treated with antibiotherapy before delivery found a prevalence of neonatal ophthalmia due to C. trachomatis of 15.2% (15/230) in newborns that received topical antibiotics for ocular prophylaxis.5 Few recent studies have investigated the perinatal transmission of C. trachomatis using NAATs, and they have reported higher rates (24%–75%), although it is difficult to compare reported rates due to the methodological differences between studies (Table 2). In Spain, assuming a prevalence of infection by C. trachomatis in women in childbirth of 1%3 and a rate of vertical transmission of 10.7%, we estimate that there would be 446 cases a year of infection in newborns (with colonisation of the nose, throat and/or eyes) based on the total births in 2015 (http://www.ine.es/prensa/np980.pdf), and that this figure would increase to approximately 750 if throat and eye swab specimens had been obtained and analysed routinely.

The rapid detection and treatment of infected newborns allowed the prevention of additional cases of conjunctivitis and future respiratory infection. We ought to highlight that in our study, all newborns received ocular prophylaxis immediately after birth. Although this intervention probably contributed to reducing the vertical transmission of C. trachomatis, it is only partially successful4 and less effective compared to its use against Neisseria gonorrhoeae. In addition, the risk of neonatal ophthalmia due to C. trachomatis is currently greater compared to the risk due to N. gonorrhoeae, as the former is more prevalent in pregnant women.3,5 For all the above reasons, the health authorities in some countries recommend screening pregnant women (which requires definition of the target population based on the prevalence of infection by age groups) and treating those infected, while the usefulness of neonatal prophylaxis remains under debate.1,3,6 Screening during pregnancy would allow the prevention of complications in the mother (pelvic inflammatory disease, sterility, etc.) and reduce the burden of disease in newborns, as maternal infection would be controlled before delivery.

In conclusion, based on our findings, we estimate that at least 1 in 1000 newborns in Spain acquires a C. trachomatis infection during birth, despite the routine implementation of ocular prophylaxis in newborns.