Short summary

There is increasing interest in sex differences in immunity during childhood. To examine differences in hospital admission rate for infections between the sexes, we conducted a register-based cohort study of all Danish residents aged 0-14 years from 1977-2014. We examined total admission rate, rates for admission by infection category, time-period, season and duration of admission according to age and sex. 

Rationale

Infectious diseases are common in pediatric patients and are a major cause of pediatric hospital admissions.  

The latest study that examined all infectious disease hospitalizations in the whole Danish population of children, was made over 10 years ago and examined the time trend in first-time admissions for infections in children aged 0-5 years from 1980-2003, but variations in admissions according to sex was not examined.

There is increasing interest in potential sex differences in immunity. Knowledge about how admissions for infections in the Danish population of children are distributed by sex, age and different infection categories, could be important for designing optimal preventive programs in both sexes and identifying potential fields for further research.

The primary aim of this study was to examine how the rate of hospital admissions for infections varies according to age and sex in Danish children. Secondarily, we examined if the variation in the rate of hospital admissions for infections according to age and sex was affected by season, type of infection, duration of admission and if admission rates changed over calendar years for categories of infections and duration of admission.

Description of the cohort

We identified our cohort through databases from Statistics Denmark. We identified 3,691,295 children aged 0-14 years eligible for participation. Of these, 1,296 (0.035%) were excluded due to lack of information on sex, giving us a cohort of 3,689,999 children. 

Criteria of inclusion:

• Age < 15 years and living in Denmark 1977
• Born in Denmark between 1 January 1977 and 31 December 2014
• Age < 15 years and immigrating to Denmark between 1 January 1977 and 31 December 2012 (No data available after 2012)

Criteria of exclusion:

• Age >= 15 years
• Emigration
• Death
• Date after 31 December 2014

Data and biological material

Registers:

• Danish Medical birth Register
• Danish National Patient Registry

Data acquired from registers:

• Infections by ICD-8 (1977-1993) and ICD-10 (1994 and onwards) codes
• Age
• Sex
• Duration of admission
• Calendar month
• Calendar year

Collaborating researchers and departments

OPEN Odense Patient data Explorativ Network, Odense University Hospital & Institute of Clinical Research, University of Southern Denmark

• Medical student Jacob W W Larsen
• Medical student Anders F Sørensen

Research Center for Vitamins and Vaccines (CVIVA), Bandim Health Project, Statens Serum Institut, Copenhagen, Denmark

• Signe Sørup, PhD
• Christine S Benn, DMSc, PhD, MD
• Aksel K G Jensen, PhD

Department of Paediatrics and Adolescent Medicine, Rigshospitalet, Copenhagen, Denmark

• Anja Poulsen, MD

Publications associated with the project

https://doi.org/10.1080/23744235.2019.1682657