Design: Difference-in-differences analysis of electronic health records, 2013–2024
Population: 1,663,441 US births after labour (202,234 caesarean)
Primary outcome: Perioperative azithromycin use and postpartum infection within 6 weeks
Effect: Azithromycin +37.6 points (33.1 to 42.2); infection −2.0 points (−2.6 to −1.4)

A JAMA study (14 September) used electronic records of 1.66 million US births between 2013 and 2024 to ask what happened after trial evidence in 2016 showed adjunctive azithromycin reduced infection after unscheduled caesarean. It compared caesarean births with vaginal births, before and after the trial, in a difference-in-differences design.

Azithromycin use at unscheduled caesarean rose from 2.2% to 39.6% (adjusted difference-in-differences 37.6 percentage points, 95% CI 33.1 to 42.2). Postpartum infection within six weeks fell from 9.2% to 8.0% after caesarean while rising slightly after vaginal birth, an adjusted difference of −2.0 percentage points (95% CI −2.6 to −1.4).

That is real-world support that the trial result travels. It also shows the gap: eight years on, six in ten eligible US patients still did not receive it. For infection teams this is a prophylaxis bundle item worth auditing.

Audit how often eligible caesareans in your unit receive azithromycin
Add azithromycin to the unscheduled-caesarean prophylaxis order set
Agree with obstetrics and anaesthesia who gives it and when
Track postpartum wound and endometrial infection before and after the change
In Indian units, where caesarean rates and post-caesarean infection are both high, the audit is worth doing

Why it matters

A proven, cheap infection-prevention step is still being missed in most eligible patients.

The statistics, in plain English

Difference-in-differences compares the change in the caesarean group with the change in the vaginal-birth group over the same period, to strip out background trends. A 2.0-point fall means about 2 fewer infections per 100 caesareans. It is still observational: other changes in caesarean care may have contributed.