[Regionally increased incidence of notified cryptosporidiosis cases due to different laboratory methods]. / Regional erhöhte Inzidenz gemeldeter Kryptosporidiosen durch unterschiedliche Laborroutinen.

ABSTRACT

INTRODUCTION: In Lower Saxony, during 2001 to 2005, 744 cases of cryptosporidiosis were reported according to the Protection against Infection Act to the Governmental Institute of Public Health of Lower Saxony. The yearly incidence rate of 1.9 notified cases per 100,000 population exceeded the German mean incidence rate of 1.5. Within Lower Saxony, there was a striking heterogeneity of regional incidences with rates greater than 10.0 in several neighbouring districts. METHODS: A retrospective case control study was conducted in cooperation with the health departments of the 5 mostly affected districts to test the hypothesis that diagnostic effects might have caused this regional cluster. Notified cryptosporidiosis cases of the years 2002 and 2003 were analysed with respect to the notifying physicians and laboratories. Notified cases of salmonellosis and campylobacteriosis were taken as controls. Controls were matched to the cases with respect to age, sex, district, and year of notification. RESULTS: Of the 146 cryptosporidiosis cases included in the case control study, 130 (89%) were diagnosed and reported by only one laboratory. In contrast, of the controls only 31% were reported by this laboratory. The matched odds ratio for this laboratory was 43.5 (95% confidence interval 10.7-177; p<0.001). DISCUSSION: The case control study revealed a significant association of the cryptosporidiosis notifications with one particular laboratory. Confounding by co-variables like age or district could be excluded due to matching. In this laboratory all stool samples submitted for routine microbiological diagnosis were screened for Cryptosporidium parvum. Diagnostic work was done by valid, specific, CE-certified procedures. We conclude that the increased regional incidence rate caused by the broader diagnostic activity of this laboratory rather reflects the real occurrence of this infection. Hence, in other regions with lower incidence rates of notified cases an underestimation can be presumed.