VALIDITY OF THE CROSS-SECTIONAL STUDY FOR THE ASCERTAINMENT OF NOSOCOMIAL INFECTION RISK-FACTORS

This study was carried out in order to assess the validity of the pure cross-sectional study in the ascertainment of nosocomial infection ri sk-factors. The results yielded by two designs (cross-sectional and ca se-control) are compared. A cross-sectional design was performed in a tertiary hospital. 592 patients were studied, 38 of whom were nosocomi ally infected. The clinical information on all the patients included i n this design was reviewed after hospital discharge. A matched case-co ntrol study was nested in the population cross-sectionally surveyed. 6 6 cases (28 additional patients developed a hospital infection) and 13 2 controls were selected. Odds ratios (ORs) for the risk factors analy zed by both designs were compared. There were no significant differenc es between the estimates yielded by both designs; however, a trend of lower OR estimates for the cross-sectional study was seen, which may b e important for risk factors not strongly related to (low relative ris k) nosocomial infection. Several factors which might account for the r esults observed (random error, bias introduced by matching) are discus sed. It is suggested that pure cross-sectional designs for the study o f risk factors of nosocomial infection may introduce a negative (towar d-the-null) bias.