Surveillance of mother-to-child transmission of HIV risk or rate in Sub-Saharan Africa
Monitoring and evaluation of Prevention of Mother-To-Child Transmission of HIV interventions in programmatic settings is part of the strategy towards elimination of new paediatric HIV infections. MTCT risk/rate is one of the recommended outcomes and its validity depends on the data collected (testing, weaning, death, loss to follow-up) as well as the statistical methods used. A systematic review conducted in 2013 highlighted that these data are not always collected, particularly weaning, and that the most appropriate analytical tools are not usually used. To improve estimation of MTCT risk/rate, PMTCT programmes should collect quality data on feeding choice and age at weaning.
A review conducted by Cock et al. in 2000 concluded that when there is no intervention and no breastfeeding, Mother-To-Child Transmission (MTCT) rates of HIV range between 15-30%. With 6 months of breastfeeding, MTCT rate increases to 25-35% and within 18 months of breastfeeding, up to 30-45% (Cock et al., 2000). Effective interventions to prevent MTCT such as triple antiretroviral prophylaxis or therapy for pregnant women living with HIV, commonly known as PMTCT options B and B+, aim to reduce the transmission rates at a point where MTCT can no longer be considered a major public health issue (WHO 2010). In breastfeeding populations, perinatal transmission rate of HIV can be decreased to less than 2% at 6 weeks and cumulative transmission rate, also known as peri- and postnatal transmission, to less than 5% at 18 - 24 months of age, a time when most infants are weaned (UNAIDS 2011). In 2011, post-breastfeeding transmission rate varied across regions of sub-Saharan Africa (SSA):
- 17% in southern Africa,
- ~21% in eastern Africa and,
- ~30% in western and central Africa (UNAIDS 2012).
This indicates that a very small proportion of women had any effective prophylaxis at all, given that the MTCT rates without any intervention is very close to those found in women thought to be enrolled in PMTCT programmes.
Standardised approach to monitor PMCTC impact
Monitoring the impact of PMTCT interventions in programmatic settings is part of the strategy towards elimination of MTCT. Impact is determined by:
- the coverage of the targeted population by the health interventions (process indicators),
- adherence to the interventions by the targeted population (intermediary indicators) and
- effectiveness (real life settings as opposed to research settings; not to be confused with effectiveness of an intervention compared to another intervention or placebo) of those interventions in the targeted population which take in consideration health systems' challenges (outcome indicators) (WHO & UNICEF 2012; WHO 2012).
The ability to monitor MTCT rates heavily depends on the data collected on a daily basis and the analytical tools used to measure the transmission rate at different time points. There are four types of data that are needed and/or used to estimate the transmission rate in a given population or a cohort of infants exposed to HIV (Dabis et al., 1993; Alioum et al., 2001; Alioum et al., 2003):
- Test results of diagnosis of HIV infection in infants at different time points: Once infected, an infant is no longer considered at risk and should thus exit the population at risk. During the analysis, the infected infants can be censored at the time of seroconversion.
- Weaning: since breastfeeding is an important risk of MTCT, the proportion of breastfed infants at each testing time should be reported. Weaning is a competing risk of HIV infection, in other words, no HIV-transmission can occur once a negative child has been weaned. In infants, seroconversion can happen 2 months after infection; this means that a definitive HIV diagnosis should be done on a blood sample taken 2 months after breastfeeding cessation. During the analysis, weaned infants can be censored, i.e. removed from the population at risk at the time of weaning.
- Death: the risk of infection ends with death in infants with previous negative results. Death by HIV and weaning status should be reported, and during analysis infants can be censored at time of death or between last negative test and death. Early death prior to first testing could be related to HIV infection;
- Loss to follow-up: infants whose diagnosis cannot be confirmed at end of follow-up. During the analysis, infants with unknown status can all be considered as negative, positive or not likely to give any new information and thus censored at the time of loss to follow-up.
All the information above is then computed and analysed using appropriate statistical methods to provide the most accurate estimate of the cumulative transmission rate. Omission of any of the four types of data listed above will result in an underestimation or overestimation of the true transmission rate.
MTCT risk/rate estimation in SSA studies
Nikuze et al. (2014) provide a brief report on a systematic review and meta-analysis on the risk of MTCT in women on triple ARVs drugs in SSA. The studies included in the review used data collected from 2002 to 2011 and were conducted in Angola, Botswana, Burkina Faso, Cameroon, Ivory Coast, Kenya, Malawi, Mozambique, Nigeria, Rwanda, South Africa, Tanzania, Uganda and Zambia. There was one population-based household survey and all the rest were facility-based studies or analysis of child testing data. Most of the studies collected information on HIV-testing, loss to follow-up, and sometimes death and feeding choice. The MTCT rates in individual studies ranged from 0 to 9.0% in infants tested at less than 3 months, 0 to 5.1%, 0 to 11% and 0 to 9.1% in infants tested from 3-6 months, 7- 15 months and 16-24 months respectively. Most of the studies used the intermediate estimate of the direct method of calculation to estimate the MTCT rate. This method assumes that infants with indeterminate HIV-status, i.e. loss to follow-up prior to last testing, dead before testing and end of follow-up, do not provide any information on the outcome. Thus, MTCT rate is estimated as = [positive] / [positive + negative] (Dabis et al., 1993). Few studies used statistical methods that allow for censoring at time of HIV infection, loss to follow-up and death.
Data on weaning is not usually collected, thus undermining the value of the risk estimate found in different populations. It is therefore important for PMTCT programmes across SSA to systematically collect quality data on feeding mode since birth and age at weaning, which should be done more than once to account for misreporting. This will ensure a standardized approach to improve the surveillance of MTCT rate (both postnatal and cumulative transmission rate).
- Alioum, A. et al. (2001). Estimating the efficacy of interventions to prevent mother-to-child transmission of HIV in breast-feeding populations: development of a consensus methodology. Statistics in Medicine, 20, pp. 3539-3556.
- Alioum, A. et al. (2003). Estimating the Efficacy of Interventions to Prevent Mother-to-Child Transmission of Human Immunodeficiency Virus in Breastfeeding Populations: Comparing Statistical Methods. American Journal of Epidemiology, 158(6), pp. 596-605.
- Cock, K.M. De et al. (2000). Prevention of Mother-to-Child HIV Transmission in Resource-Poor Countries. JAMA, 283(9), pp. 1175-1182.
- Dabis, F. et al. (1993). Estimating the rate of mother-to-child transmission of HIV. Report of a workshop on methological issues. Ghent (Belgium), 17-20 February 1992. AIDS, 7, pp. 1139-1148.
- Nikuze, A., Ekstrӧm, A.M. & Monárrez-espino, J., 2014. Risk of Mother-To-Child Transmission of HIV among Women on Triple Antiretroviral Drugs in Sub-Saharan Africa: Limitations of a Systematic Review and Meta-Analysis of Observational Studies. Online International Interdisciplinary Research Journal, iv, pp.27-36.
- UNAIDS (2011). Global plan towards the elimination of new HIV infections among children by 2015 and keeping their mothers alive 2011-2015, Geneva: Joint United Nations Programme on HIV/AIDS.
- UNAIDS (2012). Global report: UNAIDS Report on the global AIDS epidemic 2012, Geneva: Joint United Nations Programme on HIV/AIDS.
- WHO (2012). A SHORT GUIDE ON METHODS: Measuring the impact of national PMTCT programmes: towards the Elimination of New HIV Infections among Children by 2015 and Keeping Their Mothers Alive, Geneva: World Health Organization.
- WHO. (2010). PMTCT strategic vision 2010-2015: preventing mother-to-child transmission of HIV to reach the UNGASS and Millennium Development Goals, Geneva: World Health Organization.
- WHO & UNICEF. (2012). Global monitoring framework and strategy for the Global Plan towards the elimination of new HIV infections among children by 2015 and keeping their mothers alive (EMTCT), April 2012, Geneva: World Health Organization.
About the guest author
Alliance Nikuze is a Research Fellow at Desmond Tutu TB Centre, Stellenbosch University. Most of her research focus on determinants of disease/health as well as outcome evaluation. She is a public health practitioner and holds a Master of Medical Sciences in epidemiology. She can be contacted through email at firstname.lastname@example.org.
Author: Alliance Nikuze
Reviewed by: Hendra van Zyl (MPH), Jean Fourie (M.Phil) and Michelle Moorehouse (MBBCh, DA)
Date: June 2014
Nikuze, A. (2014) Surveillance of mother-to-child transmission of HIV risk or rate in Sub-Saharan Africa, AfroAIDSinfo. Issue 14, no. 6, Science. (Open access).
Last updated: 4 June, 2014