Predictive factors may be absent from many neonates with early onset pneumonia. A study of neonates in the United
Kingdom with early onset pneumonia found that risk factors were present in 78%, but in almost half (17 of 35) the only
predictor was early onset of labour.16 In India, only 40% (42 of 103) of mothers of neonates with pneumonia had identifiable
risk factors: fever, prolonged rupture of membranes
(.24 hours), leaking amniotic fluid, or foul smelling liquor.9
A problem with the methodology of the latter study is that
known risk factors are used as one criterion to define
pneumonia (box), therefore investigation of the proportion of
neonatal pneumonias with these factors is a circular
argument. Nevertheless, in this study from India, .50% of
neonates with an eventual diagnosis of pneumonia had no
known predisposing factors. This suggests that other criteria
used to diagnose pneumonia in this study were non-specific,
and the proportion of neonatal respiratory distress that was
ascribed to pneumonia (68%) is an overestimate, or that
some predisposing factors for neonatal pneumonia are
difficult to recognise.