Meta-analysis in assessment of the prevalence and annual incidence of Giardia spp. and Cryptosporidium spp. infections in humans in the Nordic countries.

We aimed to apply the meta-analysis in the studies of protozoan pathogens in order to obtain a general overview of the prevalence and annual incidence of Giardia spp. and Cryptosporidium spp. infections in asymptomatic and symptomatic human populations in the Nordic countries of Denmark, Finland, Norway and Sweden. In combining the data of 13 clinically and methodologically non-heterogeneous studies published before 2004 using the random effects model with DerSimonian-Laird estimator, we estimated the prevalence (% prevalence: 95% confidence limits) of Giardia cases in the asymptomatic (i.e. no gastroenteric symptoms) general population to be 2.97% (2.64; 3.31) and in the symptomatic population 5.81% (5.34; 6.30). For Cryptosporidium the prevalences were 0.99% (0.81; 1.19) and 2.91% (2.71; 3.12), respectively. In analyzing the data, we estimated that there will be 4670 (4300; 5060) symptomatic cases of Giardia and 3340 (3110; 3580) symptomatic cases of Cryptosporidium annually per 100,000 general population in the Nordic countries. The vast majority of cases will remain unregistered in the national registers of infectious diseases, since for single registered cases there will be 254-867 cases of Giardia undetected/unregistered and 4072 to 15,181 cases of Cryptosporidium, respectively.