Background In developed countries, male infants are more likely to be admitted to PICU and have a higher case fatality (Scott Watson et al, Am J Respir Crit Care Med, 2003). Observational studies and randomised trials in the developing world have indicated that in addition to the disease-specific protection that vaccination offers, there may also be non-specific effects including on all cause mortality (Aaby et al, PIDJ, 2007). Specifically, diphtheria–tetanus–pertussis (DTP) vaccine has been associated with poor growth and increased morbidity in girls (Agergaard et al, Vaccine, 2011).
Aims In order to understand whether this phenomenon is pertinent in the developed world, we hypothesised that non-specific vaccine effects would be demonstrated by differences in gender mortality and admission to PICU in infants with life-threatening infection.
Method Using the UK PICANET database for PICU admissions between January 2009-December 2010 we gathered a database of 16,367 male and female infants <12 months of age. We excluded planned admissions, non-infectious aetiologies, and infants where gender was unknown. We divided patients into two groups; those above and those below the age of 6 months, with the assumption that all those above 6 months of age have received their primary course of DTP/IPV immunisation. From this, we established mortality percentages for females and males admitted due to infectious causes within their age-defined groups.
Results Total infant PICU admissions due to infectious causes were greater in both male cohorts compared to female cohorts (M<6-months= 1847, F<6-months= 1277; M>6-months= 2069, F>6-months= 1580). Female mortality due to infectious causes for admission was greater than male mortality in both the under 6-month cohort (F=4.39%, M=3.09%, Odds ratio 1.44 [95% CI 0.97-2.1], chi square p= 0.056) and the over 6-month cohort (F=5.01%, M=4.81%, OR 1.05 [95% CI 0.76-1.41], chi square p=0.8).
Conclusion Our initial analysis suggests that the gender differences observed in the developing world may be mirrored in infant PICU admissions in the UK. We intend to analyse data from infants admitted with infectious aetiology over a four year period to further characterise any gender differences and potential non-specific vaccine effects.