2.3 Sample collection and selection
Thirty one hundred and ninety eight faecal specimens were collected from sporadic cases of acute gastroenteritis in patients < 5 years of age. These patients were admitted to four sites, namely Pune (Maharashtra state, n = 1007), Mumbai (Maharashtra state, n = 654), Ahmadabad (Gujarat state, n = 441), and Surat (Gujarat state, n = 1096) during the period of 2013-16. The data on RVA testing and genotyping analysis has been published earlier (Girish Kumar et al. 2020).
From a 3198 faecal specimens stored at -70°C, it was decided to test representative samples for HAdV. Assuming a 50 ±/- 5% prevalence rate of the unknown agents, the required sample size for each region was calculated to be 384. However, due to cost constraints, only 300 samples were selected at random by the Simple Random Sampling method from each region (Pune, Mumbai, Surat, and Ahmadabad). To confirm that the random sample from each region was properly representative of all samples available from that region, the expected frequencies for each parameter (age group, gender, year/month of the collection, vesikari score, and Rotavirus A (RVA) positivity) in the random sample were calculated by using corresponding percentages in the entire data. Then the observed frequencies in the random sample were compared with expected frequencies by using the chi-square test. The p-value >0.05 for each comparison showed that the random sample was properly representative of the entire set of samples in each region.