Self-sampling for analysis of respiratory viruses in a large-scale epidemiological study in Sweden.

Viral diagnosis of respiratory tract infections has so far required sampling by health professionals,hampering large-scale epidemiological studies of virus-specific disease outcomes. As part of a population-based, prospective study of work-related risk factors for transmission of viral infections (SWEDE-I), we developed a scheme for self-sampling with nasal swabs. Random selection from the gainfully employed population of a medium-sized town in central Sweden resulted in a study cohort of 2,237 men and women aged 25 to 63 years. From September 2011 through May 2012, the cohort reported all instances of respiratory tract infection or gastroenteritis and participants concomitantly sent self-sampled nasal swabs for analysis using regular mail. Diagnosis of 14 viruses was performed. A total of 1,843 samples were received. The week-wise average delay between disease on set and arrival of the specimens at the laboratory varied between four and six days, and the corresponding median delay was between 3.5 and six days. In line with previous community-based studies, picorna- and coronaviruses dominated in specimens obtained from the self-sampling scheme. The results of self-sampling were contrasted to those from contemporaneous routine clinical sampling, on the same age group, in the adjacent Stockholm county. Although higher proportions of positive samples for respiratory syncytial virus and influenza were observed in the clinical sampling scheme, estimations of seasonality for influenza A and picornaviruses derived from both schemes were similar. Our findings show that nasal self-sampling is feasible in large-scale surveillance of respiratory infections and opens new prospects for population based,virologically verified research on virus spread,burden of disease, and effects of environmental factors or interventions.

Does viral interference affect spread of influenza?

This short communication hypothesises that rhinovirus epidemics occurring after start of school may interfere with the spread of influenza during the period when warm and humid climate decreases the influenza spread by aerosol. Limited laboratory data supporting this hypothesis are included in the article, but the report is written mainly to stimulate interest and research concerning the possibility that viral interaction may affect influenza epidemiology.

Population-based rates of severe respiratory syncytial virus infection in children with and without risk factors, and outcome in a tertiary care setting.

UNLABELLED: The aim of this study was to make a population-based estimate of the risk of hospitalization and complications during virologically confirmed respiratory syncytial virus (RSV) infection in relation to established risk factors, and an estimation of additional risk factors and outcome as seen in a tertiary care referral centre. During a period of 12 y, all children with virologically confirmed RSV infection were included. Recorded complications were: admission to the intensive care unit, mechanical ventilation, death and later hospitalization for wheezing. In total, 1503 cases were identified, 1354 of which originated from the population defined by the catchment area. There was a biannual seasonal variation with late small outbreaks alternating with early large ones. The hospitalization rates for infants without risk factors were 0.8 and 1.4% during the 2 epidemic types. They were 1.6-3.2% for infants born preterm (<33 gestational wk), 2.9-7.0% for children under 2 y old with chronic lung disease of prematurity and 2.8-6.4% for infants with congenital heart disease. The presence of siblings in the family more than doubled the risk of hospitalization. Later hospitalization for wheezing occurred in 8.4 and 4.9% of children without risk factors over and under the age of 2 mo, respectively (p < 0.001). CONCLUSION: This study found lower population rates of hospitalization and complications than have previously been reported. The seasonal variation and the presence of siblings in the home influenced these rates by factors of 2.