Baseline incidence of adverse birth outcomes and infant influenza and pertussis hospitalisations prior to the introduction of influenza and pertussis vaccination in pregnancy: a data linkage study of 78 382 mother-infant pairs, Northern Territory, Australia, 1994-2015

Abstract

We conducted probabilistic data linkage of three population datasets for the Northern Territory (NT), Australia, to describe the incidence of preterm births, stillbirths, low birthweight and small for gestational age (SGA) per 1000 NT births; and influenza and pertussis hospitalisations per 1 00 000 NT births in infants <7 months of age, in a pre-maternal vaccination era. The Perinatal Trends dataset (1994-2014) formed the cohort of 78 382 births. Aboriginal mother-infant pairs (37%) had disproportionately higher average annual rates (AR) for all adverse birth outcomes compared to their non-Aboriginal counterparts; rate ratios: preterm births 2.2 (AR 142.4 vs. 64.7); stillbirths 2.3 (AR 10.8 vs. 4.6); low birthweight 2.9 (AR 54 vs. 19); and SGA 1.7 (AR 187 vs. 111). Hospitalisation (2000-2015) and Immunisation Register datasets (1994-2015), showed that influenza hospitalisations (n = 53) and rates were 42.3 times higher in Aboriginal infants (AR 254 vs. 6); and that pertussis hospitalisations (n = 37) were 7.1 times higher in Aboriginal infants (AR 142.5 vs. 20.2) compared to non-Aboriginal infants. These baseline data are essential to assess the safety and effectiveness of influenza and pertussis vaccinations in pregnant women from the NT. Remote living Aboriginal women and infants stand to benefit the most from these vaccines.

Keywords: Aboriginal and Torres Strait Islander; Australia; hospitalisations; incidence; infants; influenza; pertussis.

Fig. 1.

Data linkage study cohort for Northern Territory mothers and infants, Australia 1994–2015, inclusive. ^Individual infants included in the respective datasets who were born 1994–2015 inclusive. *Merged dataset contained uniquely identified infants from one or more of the available datasets, linked using Project Specific Linkage Key. †Infants were excluded from the final cohort if they did not have a linked perinatal record.

Fig. 2.

Low birthweight, small for gestational age and stillbirth rates per 1000 Northern Territory births, Australia (1994–2014).

Fig. 3.

Preterm birth rates per 1000 Northern Territory births, Australia (1994–2014).

Fig. 4.

Influenza hospitalisation rates per 100 000 live births for infants 0–<7 months old, by week of infant birth, Northern Territory, Australia (2000–2014).

Fig. 5.

Influenza hospitalisation rates in 0–<7 month old infants, by year of infant birth in the Northern Territory, Australia (2000–2014).

Fig. 6.

Number of pertussis hospitalisations in 0–<7 month old infants, by age in weeks of infant at time of hospitalisation and recommended pertussis vaccination schedule, Northern Territory, Australia (2000–2014).

Fig. 7.

Pertussis hospitalisation rates per 100 000 live births in 0–<7 month old infants, by year of infant birth at time of hospitalisation, Northern Territory, Australia (2000–2014).

Fig. 8.

Pertussis hospitalisation rates per 100 000 live births in 0–<7 month old infants, by age in weeks of infant at time of hospitalisation, Northern Territory, Australia (2000–2014).