A randomized, double blind, placebo controlled clinical trial was conducted in the neonatal high care unit of Tygerberg Children's Hospital (TBCH) Cape Town, South Africa for the period July 2011 to August 2012. The primary objective of the study was to assess the effect of probiotics on the incidence of NEC in high risk infants born to HIV-positive and HIV-negative women. All mothers and infants pairs that conformed to the inclusion criteria and provided written informed consent were included into the study. Premature (\<34 weeks' gestation) and very-low birth weight (\<1 250g) HIV-exposed and unexposed infants were randomized into the study or control groups by a random-number table sequence assigned by a statistician. Sample size was determined by a statistician according to the life birth statistics form the institution. Participants were enrolled and assigned to the respective groups by the researcher and two research assistants. Inclusion criteria for the mothers included: (1) HIV-positive or-negative mothers who gave birth to a premature and low birth weight baby at TBCH and consented to participate in the study; (2) Only breastfeeding mothers, regardless of their HIV status and (3) HIV-positive mothers that were on the prevention of mother to child transmission (PMTCT) treatment schedule and received nevirapine and zidovudine (AZT) as well as those that received highly active antiretroviral (HAART) medication were included in the study Babies were included if they were (1) born prematurely with a birth weight of of ≥500g and ≤1250g; (2) were HIV exposed or unexposed; (3) HIV-exposed infants and received antiretroviral (ARV) medication and (4) received breast milk (either from their mothers or donor breast milk). Breast milk of HIV-positive mothers was pasteurized (according to ward protocol) before it was administered to the infants. Infants were excluded if they had major abnormalities such as gastroschisis, a large omphalocele or congenital diaphragmatic hernia Throughout the study period, the standard of care protocol consisted of one dose (5 drops) probiotic/placebo daily for 4 weeks (28 days). This provided the study group with L. rhamnosus GG (0.35 x 109 colony-forming units \[CFU\]) and B. infantis (0.35 x 109 CFU) daily. The control group received placebo consisting of medium chain triglyceride (MCT) oil. Supplementation of the probiotic/placebo was initiated when enteral feeds started. Probiotic/ placebo supplementation was delayed/ halted in the event of: the infants being nill per os (NPO); when a query NEC was suspected the infant continued with treatment until a confirmed a positive diagnosis of NEC I was made through abdominal X-ray; if the infant remained a query NEC and was NPO the infant did not receive probiotics/ placebo until the enteral feeds were commenced again. Supplementation was discontinued when HIV-exposed infants had a positive polymerase chain reaction (PCR) result on day 14 of life.

All study participants received human breast milk. Both the probiotics and placebo were mixed with the mothers own breast milk or donor breast milk before administration via the orogastric tube or orally. The probiotic/ placebo was added to the breast milk by the researcher and two research assistants who were blinded and not involved in the routine care of the infants. Participants exited the study on day 28 after birth or upon discharge from the hospital.

Data on birth weight, estimated gestational age, gender, type of delivery, and Apgar scores were collected. Gestational age was determined by the best estimate of the neonatal and obstetrical care providers based upon physical examination of the infants. Anthropometrical measurements (weight, length and head circumference), intake and output and daily clinical progress notes were reviewed. Infants were evaluated daily for the development of NEC by the attending neonatologists. Whenever a study infant was suspected to have NEC the infant was evaluated by the attending neonatologists in conjunction with the pediatric radiologist and categorized by modified Bell's classification. Infants who developed Stage I of Bell's criteria and required surgery were exited from the study. Ethical approval was granted by the Human Research Ethics Committee of the Faculty of Health Sciences, Stellenbosch University and Tygerberg Academic Hospital. The clinical trial registration number: DOH-27-0413-4277. Data analyses were performed with Statistica Software (version 11). Frequencies between groups were compared using the likelihood ratio chi-square test and means between groups using t-tests. Statistical significance was defined as a p-value less than 0.05.