Introduction
Pregnant women and neonates are at high risk of developing sepsis. In both groups, the risk persists for several weeks post delivery, and is associated with significant mortality [
1,
2]. Morbidity due to maternal and neonatal sepsis is particularly high in sub-Saharan Africa (SSA) [
3].
Globally,
Staphylococcus aureus and Group B Streptococcus (GBS) are the main causes of maternal and neonatal sepsis [
4‐
6]. However, Group A Streptococcus (GAS;
Streptococcus pyogenes) is increasingly recognized as an important Gram-positive pathogen associated with maternal and neonatal sepsis [
7‐
9]. GAS can cause both early and late onset of neonatal sepsis [
10,
11], usually as a result of infection acquired through the birth canal [
11]. GAS also causes non-invasive disease, including tonsillo-pharyngitis, skin infections and rheumatic fever that can result in rheumatic heart disease [
12‐
14].
In high-income countries, it is estimated that the annual incidence of GAS-related maternal sepsis is 6 per 100,000 live births, with a 3.5% case-fatality ratio for invasive disease [
15], and the incidence of GAS neonatal sepsis is 1.5 per 100,000 person years [
16]. There is limited data on the burden of GAS infections in SSA due to the lack of systematic surveillance [
17]. In the Eastern Cape, South Africa, the mean annual incidence rate of invasive GAS infection was 6 cases per 100,000-person years in all age groups (58% of samples from 18 to 64 year olds) [
12]. In Kenya, the incidence of neonatal GAS sepsis was 0.6 cases per 1000 live births [
18].
GAS colonizes the posterior pharynx and or skin of asymptomatic individuals who, although can transmit the bacterium, are less likely to transmit it than those with an acute GAS infection [
19]. Understanding antibiotic resistance of GAS colonization is an indirect measure of understanding resistance of GAS causing acute infection in the community. In addition, there have been reports of an increased risk of neonatal infections associated to maternal vaginal carriage of GAS in the early postpartum period often with poor outcomes for these infants [
20].
Here we present a posthoc analysis of the PregnAnZI trial [
21] to determine the effect of 2 g intra-partum azithromycin on prevalence and antibiotic resistance of GAS in mothers and their newborns during the 4 weeks following prophylactic treatment. Whole genome sequencing (WGS) was done to further characterise the GAS isolates and perform phylogenetic analysis to explore the differences in the effect of azithromycin between anatomical sites.
Discussion
One oral dose (2 g) of azithromycin given to women in labour reduced occurrence of GAS carriage among women and their babies in the nasopharynx and breast milk without an increase of azithromycin resistance in isolates in these sample sites. In contrast, the intervention did not have any effect on the occurrence of GAS carriage in the vaginal tract but induced an increase in the carriage occurrence of azithromycin resistant SDSE(A).
Previous results from this study have shown that a single oral dose (2 g) of azithromycin given to women in labour reduced the prevalence of
S. aureus, S. pneumoniae and GBS carriage in the mother (nasopharynx, breast milk and vaginal tract) and the baby (nasopharynx) [
21]. The current analysis shows that the intervention also reduced the prevalence of GAS carriage in the breast milk and nasopharynx of study women and, less clearly, in the nasopharynx of their newborns. Despite substantial reduction of GAS carriage, we did not observe any short-term increase of azithromycin resistance in these two anatomical sites.
Conversely, the intervention did not have any effect on the prevalence of GAS carriage in the maternal vaginal tract but induced an increase in azithromycin resistance. WGS revealed that GAS vaginal carriage in the azithromycin arm was primarily due to azithromycin-resistant SDSE(A), whereas in the placebo arm, GAS vaginal carriage was entirely due to azithromycin-susceptible
S. pyogenes. In our previous analysis on
S. aureus, lower reduction in carriage in the vaginal tract alongside a higher prevalence of resistance was also observed [
21]. It is not clear why the effect of the intervention in the vaginal tract differs from other body sites. The concentration of azithromycin in the vaginal tract may be lower and fall more rapidly than in other anatomical sites. We had previously shown a very high concentration of azithromycin in breast milk during the 4 weeks following the intervention, with a peak during the first 6 days (concentration > 4000 µg/L) [
29]. A different study using a single dose of azithromycin (1 g) showed the azithromycin concentration in the vaginal tract was much lower than the breast milk concentration we observed [
30]. In this study, the peak concentration occurred during the first 24–48 h following the intervention [
30], long before the post-intervention VS were collected in our study. It is possible that removal of
S. pyogenes from the vaginal tract allows azithromycin-resistant SDSE to thrive, whereas in other anatomical sites higher concentrations of azithromycin can overcome the efflux-mediated resistance mechanisms [
31]. An alternative explanation is that even though SDSE can be found in different anatomical sites, it is better suited to survive in the vaginal tract [
32]. One azithromycin resistant SDSE(A) was isolated in the vaginal tract from a woman included in the azithromycin arm before the intervention was administered. A phylogenetically linked isolate was isolated from the same woman’s VS after the intervention (Additional file
1).
The public health and clinical implications of the selective expansion of SDSE(A) in the vaginal tract are difficult to anticipate. However, similarly to
S. pyogenes, SDSE can cause invasive disease [
33‐
35]. Lancefield group A SDSE has been described in previous studies from high income settings, including a collection of isolates causing invasive disease in the USA [
27]. The SDSE(A) isolated from our study participants have distinct phylogeny to SDSE(A) previously isolated in USA and fall into two distinct clades. In our study, all SDSE(A) isolates harboured
mefA-msrD genes, whereas both
erm(B) and
mefA-msrD genes were found in azithromycin-resistant
S. pyogenes isolates. While the presence of
mefA is associated with macrolide resistance,
msrD has a more dominant role [
36,
37]. The presence of both
mefA and
msrD may confer high level resistance [
37].
The trial was designed to evaluate the effect of intra-partum azithromycin on maternal and neonatal carriage of
S. aureus,
S. pneumoniae and GBS that are more prevalent than
S. pyogenes and therefore the current analysis was underpowered as observed in the comparison of trial arms in the nasopharyngeal swabs, especially in newborns, as carriage of GAS is lower than for those other bacteria. This was an opportunistic study and oropharyngeal rather than nasopharyngeal samples may have been more appropriate for detecting
S. pyogenes carriage where it would be expected that carriage would have been slightly higher [
38]. In any case, the objective of the analysis was to assess the impact of the azithromycin on GAS carriage and there is no reason to believe this should be very different in the oropharynx when compared to the nasopharynx. Overall, our study adds to the growing evidence that GAS may include SDSE as well as
S. pyogenes.
Acknowledgements
The authors express our profound gratitude to the study participants and their families for agreeing to take part in the study. We give special thanks to the laboratory team (Njemmeh Manneh, Aji Mary Taal, Aru Kumba Baldeh, Modou Lamin Fofana, Momodou Abass Bah and Nano Kora) for their involvement in sample reception and processing. We also extend our gratitude to Jarra Manneh and Abdoulie Kanteh of the MRCG genomics team, Nuredin Ibrahim Mohammed for assisting with generating some Figures and the field team (led by Edrissa Sabally and Omar Jarra) for assisting with sample collection.
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