Chorioamnionitis and NEC – the challenge of significant small associations

Cover imageIn a recent flurry of twittering, Archimedes noticed a meta-analysis linking chorioamnionitis with necrotising enterocolitis. Although a long time since doing neonates has passed, the consequences of NEC were profound enough to stick, and a potential association, perhaps a route in to stopping it happen, would be welcome.

The meta-analysis showed that, on univariate examination, there was a positive relationship between clinical chorioamninonitis and significant NEC (Bell stage 2 or worse), with an OR of approximately 1.3.

To convert this to something more clinically useful – say, the proportion of chorioamnionitis-born-babies who’d develop NEC, and the proportion who didn’t have a mum with CC but got NEC anyway – needed to know approximate average rates of NEC and CC.

A large multicentre US study by Yee helps us out here, with around 5% of preterm infants getting NEC and about 11% on non-NEC babies having mums with CC. Popping these values into a theoretical cohort of 1000 neonates leads to:

NEC Not
CC 7 105
Not 43 845
50 950

The positive predictive value of CC for NEC is about 6.2%, and the rate of ‘unsuspected’ NEC in the non-CC group would be 4.8%

This highlights the trouble with relative measures of association in relatively rare conditions; you don’t actually end up knowing a lot more than when you started.

Archi

(Many thanks for the leads into this from @PaedsRH and @Jfphol)

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