Key drivers of cloud response to surface-active organics.

Aerosol-cloud interactions constitute the largest source of uncertainty in global radiative forcing estimates, hampering our understanding of climate evolution. Recent empirical evidence suggests surface tension depression by organic aerosol to significantly influence the formation of cloud droplets, and hence cloud optical properties. In climate models, however, surface tension of water is generally assumed when predicting cloud droplet concentrations. Here we show that the sensitivity of cloud microphysics, optical properties and shortwave radiative effects to the surface phase are dictated by an interplay between the aerosol particle size distribution, composition, water availability and atmospheric dynamics. We demonstrate that accounting for the surface phase becomes essential in clean environments in which ultrafine particle sources are present. Through detailed sensitivity analysis, quantitative constraints on the key drivers - aerosol particle number concentrations, organic fraction and fixed updraft velocity - are derived for instances of significant cloud microphysical susceptibilities to the surface phase.

Healthcare-associated rotavirus gastroenteritis in a large paediatric hospital in the UK.

Rotavirus is a major cause of acute, community-acquired gastroenteritis in infants and young children but its importance in healthcare-associated paediatric gastroenteritis is much less well understood. A prospective study was undertaken at the Royal Liverpool Children's NHS Trust, Liverpool, UK. We enrolled 243 children with acute gastroenteritis (AGE) who were hospitalised between January and May 2006. Rotavirus was detected in faecal specimens by enzyme immunoassay. This virus was responsible for 17/91 cases (19%) of healthcare-associated AGE and 54/152 cases (36%) of community-acquired AGE. Sixteen children with healthcare-associated acute rotavirus gastroenteritis required source isolation and eight received intravenous rehydration. We conclude that rotavirus is an important cause of healthcare-associated AGE in a large paediatric hospital. Rotavirus vaccines represent a public health tool that could prevent the majority of symptomatic rotavirus infections within this healthcare setting.