A longitudinal study into the correlation between faecal urease activity and incidence of nappy rash in infants

ObjectivesThe objective of this study was to look at whether there is a correlation between urease activity in babies faeces and observed incidence of nappy rash (diaper dermatitis) in a six-infant longitudinal observational study conducted at a university childcare facility over 9 months. MethodsSix babies who met the inclusion criteria and who attended Westwood Nursery, University of Bath were recruited to the study with consent provided by parents following favourable ethical committee opinion from the NHS Regional Ethics Committee. Soiled nappies donated up to twice weekly were analysed for the urease activity in faecal bacteria. At the same time, Nursery staff recorded the skin condition of the nappy area of participating infants. ResultsA clear statistical correlation between urease expression and observed nappy rash incidence and absence of faecal urease and healthy skin was observed using Chi squared analysis (P = <0.0001). ConclusionsUrease expressing bacteria were first implicated in the pathogenesis of nappy rash in the early 20th century. This is the first study to show a population level correlation between nappy rash and faecal enzyme activity, which can be understood in terms of a causal chain: urease catalyses ammonia production, which directly damages skin barrier function and creates a pH environment in which secondary opportunistic micro-organisms can grow at an enhanced rate and increase skin damaging enzyme activity, therefore leading to more severe nappy rash. Key messagesO_ST_ABSWhat is already knownC_ST_ABSthe involvement of urease /ammonia expressing bacteria in the pathogenesis of nappy rash has been suggested for over 100 years. What this study addsThis study shows a clear temporal correlation between faecal urease expression and nappy rash incidence (and vice versa) in a group of six infants followed over 8 months suggesting the key importance of urease in nappy rash pathogenesis in a relevant study population and adds to a previous causal mechanism, where urease converts urea to ammonia, which has been shown to both directly damage skin barrier function and raise skin pH. How this study might affect research, practice or policyThis study raises the possibility that nappy rash can be treated more effectively by direct inhibition of urease. Several urease inhibiting strategies are currently being studied, including watercress extract and probiotic bacteria.