Incidence and comparison of retrospective and prospective data on respiratory and gastrointestinal infections in German households

BACKGROUND: Acute respiratory infections (ARI) and acute gastrointestinal infections (AGI) are the most common childhood infections, and corresponding data can either be collected prospectively or retrospectively. The aim of this study was to estimate the incidence of respiratory and gastrointestinal episodes in German households with children attending day care and to compare results of prospective and retrospective data collection. METHODS: We conducted a 4 months prospective cohort study in the winter period 2014/2015 and recruited parents of children aged 0–6 years in 75 day care centers in Braunschweig, Lower Saxony, Germany. For all household members, we collected information on episodes of ARI and AGI. We applied prospective data collection in one study arm and retrospective data collection with a reporting period of 2 months in the other. Poisson regression was used to model monthly incidence rates for both study arms. RESULTS: In total, 100 households (including 404 persons) participated in the retrospective group and 77 households (282 persons) in the prospective group. Incidence estimates for ARI (retrospective group: 0.52 per person month, prospective group: 0.47) were higher than for AGI (retrospective group: 0.14, prospective group: 0.13). The adjusted incidence estimates were similar in both study arms for ARI (incidence rate ratio for retrospective versus prospective data collection: 1.11 [confidence interval (CI) 95% 0.99; 1.24], p = 0.42) as well as for AGI (1.10 [CI 95% 0.89; 1.37], p = 0.27). CONCLUSION: If there is no need to collect biomaterials or data on severity of the diseases, incidence of infections in the household setting over a short time period (2 months) can be assessed retrospectively. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12879-017-2434-5) contains supplementary material, which is available to authorized users.