Table 4.

Evidence for antibacterial resistance (ABR) following MDA-azithromycin

Infection	Resistance evidence
Trachoma	•Three observational studies in Tanzania and Ethiopia assessed antibacterial resistance in C. trachomatis following one to four rounds of MDA-azithromycin. None of the studies found evidence of macrolide-resistant C. trachomatis 2–18 months after final treatment, although non-standard microbiological protocols were used in all studies [55]
Yaws	•In a region in Papua New Guinea where MDA-azithromycin was administered (with coverage of 84%) followed by targeted treatment programs, five cases of active yaws demonstrated clinical failure with azithromycin. Polymerase chain reaction (PCR) testing detected the A2059G mutation, a 23S rRNA mutation that can confer high-level resistance to macrolides and that is also found in T. pallidum pallidum. Interestingly, all clinical failures were detected among boys in the same village, thus the authors hypothesized that a de-novo mutation had arisen in one participant’s isolate and then been transmitted to others [54]
Streptococcus pneumoniae	•S. pneumoniae resistance to macrolides with MDA-azithromycin was documented as early as 1995 in children treated with a single dose of azithromycin for trachoma control, with 1.3% of children’s isolates showing resistance before and 21.3% of children’s isolates showing resistance up to 2 months after treatment [6] •A systematic review of studies through June 2018 found 19 studies exploring ABR after MDA-azithromycin, with 12 studies on S. pneumoniae. Baseline values of S. pneumoniae macrolide resistance prevalence in 6 studies ranged from 0 to 35.8%. Studies showed an increase in prevalence followed by a decrease, no increase after MDA-azithromycin, or no resistance at both time points [55] •Among children from Niger in MORDOR I, the proportion with S. pneumoniae macrolide resistance was higher in the MDA-azithromycin group (12.3%) compared to placebo (2.9%) after 4 rounds of treatment, indicating a four-fold rise [63] •In a subset of the Tanzanian group in MORDOR I, the proportion of macrolide-resistant S. pneumoniae isolates in children treated with azithromycin versus placebo at baseline (end of treatment), 12 months later, and 24 months later were 26.5%, 26.8%, and 13.4%, respectively, compared to 13‒18% in the placebo groups [59] •In a study exploring the impact of MDA-azithromycin with seasonal malaria chemoprophylaxis in Burkina Faso, there was increased S. pneumoniae resistance in several serotypes but resistance did not seem to favor one serotype in particular. Four serotypes 35B (2%), 23F (0.9%), 19F (0.9%), and 6A (0.7%) had the most macrolide-resistant isolates [90]
Staphylococcus aureus	•Three MDA-azithromycin rounds in the Gambia (PRET sub-study) were associated with a short-term increase in the prevalence of macrolide-resistant or macrolide-inducible, clindamycin-resistant S. aureus. Macrolide resistance was attributed to the presence of the msr and erm genes [56] Resistance dropped after cessation, but not to baseline levels [2]
Streptococcus pyogenes	•In a study of combined ivermectin and azithromycin compared to ivermectin alone in the Solomon Islands, there was no macrolide resistance detected in S. pyogenes at baseline, 3 months, or 12 months [57]
Enteric Organisms	•One RCT from Tanzania showed that a single round of MDA-azithromycin was associated with a substantial increase in macrolide-resistant E. coli, especially in younger children and those with prior diarrhea. Carriage prevalence decreased over time, but macrolide resistance remained elevated over baseline levels 6 months after dosing (from 21% at baseline to 61% at 1 month and 31% at 6 months) [58] •In a subset of the Tanzanian cohort from MORDOR I, at baseline, 12 months, and 24 months, the proportion of azithromycin-resistant E. coli isolates in the azithromycin arms increased transiently and then decreased (14.9%, 21.5%, and 14.9%, respectively, compared to 14–19% in the placebo arm) [59] •One study from Tanzania showed 17% of E. coli isolates from rectal swabs of children born after the last of 4 MDA-azithromycin rounds were resistant to azithromycin [91] •The Niger arm of MORDOR I showed determinants of macrolide resistance in the intestinal flora were higher in the MDA-azithromycin group (68.0%) compared to placebo (46.7%) at 6 months after 4 twice-yearly treatments with MDA [60] •Longer-term assessments among children in Niger were conducted while twice-yearly mass administration was occurring [61] Determinants of macrolide resistance remained higher in the azithromycin group compared to the placebo group: 7.4 times as high at 36 months and 7.5 times as high at 48 months

MDA mass drug administration, MORDOR Macrolides Oraux pour Réduire les Décès avec un Oeil sur la Résistance, PRET the Partnership for Rapid Elimination of Trachoma, RCTs cluster randomized trials, TANA Trachoma amelioration in Northern Amhara