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Maternal viral load and vertical transmission of HIV-1: an important factor but not the only one

The European Collaborative Study

Epidemiology and Social: Original Papers

Objectives: To investigate the association between maternal RNA load, risk of vertical transmission of HIV-1, and other variables.

Methods: Plasma or serum samples from mothers of 373 children, enrolled in the prospective European Collaborative Study, were collected around time of delivery, and HIV-RNA quantified using two types of commercial assay. Women and children were followed according to a standard protocol. Adjusted odds ratios (AOR) were calculated to estimate the effect of RNA load and other maternal factors on vertical transmission.

Results: Maternal RNA levels, mode of delivery and gestational age were independently associated with transmission. Vertical transmission increased with increasing RNA levels, but there was no threshold below which transmission did not occur. The risk was more than double for women with RNA above the sample specific median [AOR 2.36 (1.23-4.52)]. Elective caesarean section was associated with a substantial and significant decrease in transmission [AOR 0.19 (0.06-0.55)], and delivery before 37weeks gestation with an increased risk [AOR 2.67 (1.33-5.38)]. Elective caesarean section was effective in both subgroups defined by median RNA level [AORs 0.37 (0.08-1.71) and 0.15 (0.03-0.64) below and above median respectively]. The predicted rate of transmission in a woman with a low RNA load delivering by elective caesarean section or vaginally after 37weeks is around 2%, and 11%, respectively.

Interpretation: Mother-to-child transmission of HIV-1 is multi-factorial; high RNA load is an important determinant but clearly not the only one. Interventions that target risk factors other than maternal RNA load remain important.

From *The European Collaborative Study (for a list of these collaborators see Appendix). Prepared by Andrea Bailey, Marie-Louise Newell, Catherine Peckham (ECS Coordinating Centre, London, UK), Anita De Rossi (Institute of Oncology, University of Padua, Italy), Anneka Ehrnst (Karolinska Institute, Stockholm, Sweden), Ilse Grosch-Wörner (Charite Virchow-Klinikum, Berlin, Germany), Oriol Coll (Hospital Clinic, Barcelona, Spain) and Frank De Wolf (Amsterdam Medical Centre, The Netherlands).

Requests for reprints to: Dr Marie-Louise Newell, Department of Epidemiology and Public Health, Institute of Child Health, 30 Guilford Street, London, WC1N 1EH, UK.

Sponsorship: This study is a concerted action of the European Commission (PL 962005). The Medical Research Council (UK) provides support to the coordinating centre. Collaborating centres were supported by grants from the Ministero della Sanita-Istituto Superiore di Sanita, Progetto AIDS (Padua, Genoa); the Medical Research Council (UK), the AIDS Virus Education Research Trust, the Scottish Office Home and Health Department (Edinburgh); Praeventiefonds number 28-1704 (Amsterdam); Fonds Houtman, Office de la Naissance et de L‚Enfance, Communaute Francaise de Belgique (Brussels), and the Swedish Medical Research Council (Stockholm).

Received: 12 February 1999; revised: 19 April 1999; accepted: 26 April 1999.

Copyright © 1999 Wolters Kluwer Health, Inc.