2.3 Study Design and Method: Case-control study 62
2.3.3 Study Method 63
2.3.3.1 Definitions of case and control subjects:
Case subjects were defined as an infant <90 days old with GBS confirmed by culture on
blood, CSF or other normally sterile site, or by latex agglutination of CSF. These cases were identified by daily surveillance, with the assistance of microbiology and/or paediatric staff. EOD was defined as isolation of GBS within the first 6 days of life. LOD was defined as isolation of GBS from days 7-89 after birth.
Control subjects: To match for cases of EOD, healthy neonates were enrolled within the first 6
days of life and followed through to ensure they remained free of invasive GBS disease until 90 days of age. Secondly, to match for cases of LOD, we enrolled infants born within 14 days (but >7 days of life) to the day of the case subject and who did not develop invasive GBS disease. All controls were further matched to cases for gestational age at birth (within 2 weeks of the gestational age if the case was born prematurely (<37 weeks gestation) and to term if the case was born at ≥37 weeks gestational age, maternal HIV-infection status, maternal age (within 2.5 years of the case mother’s age).
2.3.3.2 Assessment of gestational age:
In order to achieve accuracy, gestational age at birth was calculated using the following hierarchal tools.
1) The gestational age at birth was estimated from an ultrasound examination performed before 24 weeks gestational age.
2) If the mother did not have an ultrasound examination performed before 24 weeks gestational age, gestational age staging was undertaken using the Ballard score completed within 24 hours of birth by the attending doctor or study staff.
3) If the mother/infant did not have either of the above undertaken and was certain of her last normal menstrual period (LMP), this was used to stage the gestational age. 4) In the absence of any of the above methods for calculating the gestational age at
birth, we used any available ultrasound examination (≥24 weeks) to calculate the gestational age.
5) If none of the above methods were available, then either the symphysis fundal height (SFH) at the time of labour was used, or the newborn was classified as being “term” if the birth weight was more than 2500 grams.
2.3.3.3 Method for recruitment of Case subjects:
Daily in-person audits with the National Health Laboratory Service (NHLS), Department of Microbiology and/or attending physicians were undertaken at CHBAH, CMJAH and RMMCH to identify cases of Streptococcus agalactiae from a sterile site. The mother was approached for consent and enrolment of her child and herself within 72 hours of the culture result becoming available. We attempted to enrol cases within a maximum period of 120 hours from the time the culture as delay in enrolment could have affected antibody measurements.
Procedures conducted at the time of enrolment (Table 2.3):
Maternal and infant case report forms were completed by the study doctor or nurse. Maternal and delivery history including identifiable risk factors for GBS were obtained
from the mothers and from the available clinical records. For those mothers who delivered at one of the site hospitals, the maternal files were extracted for data. Furthermore, examination of the mother, the use of IAP and maternal blood results including HIV status and CD4+ T-lymphocyte counts were recorded.
Infant’s history, examination, routine blood results and in-patient management were recorded from the infants hospital file.
Bloods was taken from the mother (5mL) and infant (1-2mL) to measure antibodies to the four common CPS serotypes (Ia,Ib,III,V), and 5 proteins; 3 pilus proteins (PI-1, PI- 2a and PI-2b), FbsA and BibA.
The mother was swabbed (rectal and lower vaginal) for GBS culture and sero-typing. A clean-catch midstream urine specimen was taken for GBS culture.
The mother was given a copy of the informed consent form and a card with a follow- up date to return at the next visit.
Specimens were transported at room temperature to the laboratory at the Respiratory and Meningeal Pathogens Research Unit (RMPRU) for processing within 6 hours or otherwise refrigerated for 24-48 hours.
Table 2.3: Schedule of visits and procedures on participants in the study
Schedule of visits Visit 1 Visit 2 Visit 3 Visit 4
Time Period GBS1 culture positive or Control (enrolment) 4 weeks post delivery (±1week) (21-35 days) 12 weeks post delivery (±1week) (77-91 days) 24 weeks post delivery (±1week) (161-175 days) ICF2signed X
Inclusion/ exclusion/ Withdrawal
criteria X
Medical history (Mom) X
Targeted physical exam (Mom) X
Medical history (infant) X X X X
Physical examination (infant) X X X X
Denver-II developmental assessment
(infant) X X X
Swabs (rectal &vaginal) for GBS
culture (Mom) X
Urine culture (Mom) X
Maternal Blood for antibodies
(Capsular, Pilus, FbsA and BibA) X
Cord/Infant Blood for antibodies
(Capsular, Pilus, FbsA and BibA) X
1GBS-Group B Streptococcus; 2ICF- Informed consent form
During the study, it was increasing difficult to enrol mothers whose newborn had demised from invasive GBS disease prior to the culture result becoming available. Once the culture result became available, the mothers were telephonically contacted to inform them of the disease as well as advise them on future preventative measures. The Ethics Committee also approved us retrospectively collecting clinical data from the medical records and run antibody analysis on residual sera at NHLS taken at the time of admission of the cases, in the event that consent was unavailable from the parent of the child.
Case recruitment started on the 7th November 2012 and ended on the 6th November 2013. Over the twelve month period, 126 cases of invasive GBS disease were identified from the three academic hospitals (Figure 2.1). We obtained consent from and enrolled 99 mother-infant pairs whilst data was retrospectively collected on a further 27 infants. Four subjects were excluded from the analysis, including two with recurrent episodes of invasive GBS disease, one case in which the culture result was revised to be Streptococcus viridans and one case which occurred in a 120 day old infant. Consequently, 122 invasive GBS disease cases were analysed, of which 119 isolates were serotyped. The cases in which serotypes were
unavailable included two cases in which GBS was identified only on bacterial latex antigen and one case in which the isolate was not retrieved. For the antibody analysis, infant blood was unavailable on 10 subjects. Furthermore, we excluded two enrolled cases that had blood samples taken >120 hours from the date of culture and four infants in whom we were unable to enrol suitable matched controls. Therefore, serum was available from 103 infants (including 1 set of twins) and 89 mothers (Figure 2.1).
Excluded from overall analysis
Not GBS (n=1) >90 days (n=1)
2nd episode of GBS (n=2)
Excluded from antibody analysis
Not serotyped (n=3) No serum/plasma (n=10) Serum obtained late (n=2) No matched control (n=4)
Figure 2.1: Schematic representation of cases presenting at the three sites
Footnote: CHBAH-Chris Hani Baragwanath Academic Hospital; CMJAH-Charlotte Maxeke Johannesburg Academic Hospital; RMMCH-Rahima Moosa Mother and Child Hospital; EOD-early onset disease; LOD-late onset disease.
Overall n=126 EOD= 66 LOD=60 CHBAH n=84 EOD=47 LOD=37 CMJAH n=22 EOD=11 LOD=11 RMMCH n=20 EOD=8 LOD=12 99 mother- infant pairs enrolled 27 infants- retrospectively collected data 26 EOD=17 LOD=9 96 EOD=49 LOD=47 90[mother/infant pairs] EOD=47 LOD=43
13[only infant blood]
EOD=9 LOD=4 CHBAH n=69 EOD=40 LOD=29 CMJAH n=16 EOD=8 LOD=8 RMMCH n=18 EOD=8 LOD=10 Overall n=103 EOD= 56 LOD=47 Total GBS cases-103 EOD (n=56): <34=15; ≥34=41 LOD (n=47): <34=6; ≥34=41 Total GBS cases-122 EOD (n=66): <34=22; ≥34=44 LOD (n=56): <34=8; ≥34=48 Informed by microbiologist or physician about invasive GBS
2.3.3.4 Method for recruitment of control subjects matched for EOD
Controls were recruited over a fifteen month period from the 13th November 2013 to the 12th February 2014 during normal working hours at CHBAH only. Mothers in labour were
screened to match the above criteria. Cord blood was collected during delivery and stored until the mother was clinically stable (±4 hours). Mothers of healthy neonates were identified, informed about the study, given an opportunity to read and sign the informed consent form and thereafter consented if willing to participate in the study. If the mother declined, the cord blood was discarded. In a minority (<5%) of deliveries, cord blood was not obtained and the mother was consented to obtain blood from the neonate within 72 hours of birth. The rest of the procedures conducted at the time of enrolment were the same as those mentioned in chapter 2.3.3.3 above. Audits of the microbiology laboratory continued three months after enrolment of controls ended to monitor whether any of the controls may have subsequently developed invasive GBS disease. Controls were also interviewed at the 3 month visit to confirm they were not hospitalized with sepsis.
2.3.3.5 Method for recruitment of control subjects matched for LOD
These infants were recruited from the community, except for the otherwise healthy premature infants who were also enrolled from the neonatal wards provided they had not been previously diagnosed with sepsis and the reason for hospitalization was only for feeding support and weight gain. Mothers of healthy infants were identified in the postnatal wards and given specific dates on which to return to the RMPRU clinic for enrolment. In addition, the maternity birth registers were used to identify mothers who were discharged with their baby after delivery and fulfilled the matching criteria. The contact numbers of these mothers were
sourced from the hospital patient registry. At the RMPRU clinic, mothers were informed about the study, given an opportunity to read the informed consent form and consented if agreeable to participate. The procedures carried out on the mother and infant were the same as for those listed for the cases in chapter 2.3.3.3 above.
2.3.3.6 Follow-up visits of cases and controls
Both cases and controls were followed up at 1, 3 and 6 months of chronological age at the RMPRU (Table 2.3). Those subjects who failed to attend the schedule visit within 14 days of the infants scheduled visit were excluded from the analysis of that age, whereas some were completely lost to follow-up because they did not attend any follow-up visits. For those children who did not attend follow-up, attempts were made to maintain the timing of the visit by contacting the next of kin, using alternative telephone numbers provided and by conducting home visits.
The follow-up visits were conducted by one of two trained research assistants, an enrolled nurse or a study doctor (myself or RMPRU medical officer). All cases and controls assessed as having developmental delay were additionally evaluated by a study doctor (myself or RMPRU medical officer). At these visits, a directed medical history and examination was conducted on the infant with particular neurodevelopmental focus. The Denver Developmental Screening Test II (Denver-II) (Appendix 7) was used to identify infants with suspected developmental delay. In addition, infants with hypertonia and/or hydrocephalus were categorised as having abnormal neurological findings. Infants diagnosed with neurological abnormalities were
referred for further care, including for occupational, physio and speech therapy. No blood samples were taken at these visits.
In 1992, the Denver-II was modified from the original Denver Developmental Screening Test which was developed in 1967 (Frankenburg et al., 1992). The Denver-II is a broadly accepted screening tool for developmental delay and has been approved by the American Academy of Pediatrics. The Denver-II, however, is not diagnostic or a predictor of later developmental delay. The Denver-II makes a valuable screening tool reaching sensitivities of 83% (Glascoe et al., 1992), which has been demonstrated to have high degree of intra- and inter-examiner correlation (Frankenburg et al., 1992). Furthermore, as the normal development of a child may be wide-ranging within ages, a percentile range based on growth and milestone curves in which each developmental test item may be accomplished is provided (Frankenburg et al., 1992, Shahshahani et al., 2010).
The Denver II includes 125 test items in 4 domains: gross-motor (32), fine-motor (29), language (39) and personal-social (25). An age line is drawn vertically corresponding to the age of the infant. For premature infants, an adjustment for the number of weeks to term is undertaken. At least three items to the left and three to the right of the age line are assessed in each of the four domains. Each test item is represented horizontally as a percentile age range (25-90%) for which it is estimated that the item can be achieved. The scoring system for the test items are graded as follows;
“pass”- the infant performed the item or the caregiver reported this “fail”- the infant did not perform the item or the caregiver reported this
“no opportunity”- the infant has not had the chance to perform the item as reported by the caregiver
“refusal”- the infant refused to attempt the item.
A “fail” or “refusal” by the infant in an item to the left of the age line was classified as a “delay”, whilst a “fail” or “refusal” by the infant in an item through the 75-90% age percentile was classified as a “caution” (Figure 2.2). The final result was then scored as “normal” (no delays or 1 caution) or “suspect” (≥2 cautions or ≥1 delay) in each of the four domains.
Figure 2.2: Interpretation of Denver-II scoring system (adapted from the Denver II screening test)