Reduction of rotavirus as a cause of nosocomial diarrhoea in northern Stockholm after introducing the rotavirus vaccine

<b>Background:</b> Vaccination against rotavirus was offered in Stockholm to children born on 1 March 2014 and onwards with 85% coverage after two years. We investigated changes in nosocomial diarrhoea 2010—2018 in children admitted to Astrid Lindgren Children’s Hospital, Stockholm, Sweden. <b>Methods:</b> We retrospectively identified cases from diagnostic and virology department registers. Complications and chronic medical conditions were retrieved from the case records. Children &lt;18 years of age who developed diarrhoea ≥48 h after admission for another diagnosis and had a faecal sample submitted to the virology department were included. <b>Results:</b> There were 474 episodes of nosocomial diarrhoea. Of these, 401 (85%) occurred in children with chronic medical conditions. In children &lt;5 years the rates of nosocomial rotavirus gastroenteritis, with 95% confidence intervals, significantly decreased from 0.34 (0.25—0.45) per 100 admissions prevaccination to 0.09 (0.04—0.17) postvaccination and from 0,66 (0.48—0.88) to 0.16 (0.07—0.30) cases per 1000 hospital days. Postvaccination norovirus became the most frequent pathogen. Virus-positive cases were more common in young children and in winter months. <b>Conclusions:</b> Before the initiation of rotavirus vaccination, norovirus and rotavirus were equally common causes of nosocomial diarrhoea. Postvaccination, rotavirus was reduced by approximately 75% while the frequency of other viruses did not change.