[The use of incidence density in assessing the risk factors for nosocomial infection]. / Utilización de la densidad de incidencia en la valoración de factores de riesgo de la infección nosocomial.

Several authors have suggested that incidence density should be used in studying nosocomial infection. We assess several risk factors for hospital infection by two ratios, the incidence density ratio (IDR) and the relative risk (RR), in an historical cohort of 843 patients. The variables analyzed were: operation, its length, type of surgical wound, severity of underlying disease, and age. The IDR figures were always lower than those yielded by the RR. For example, the IDR for operated patients was 2.78, whereas RR yielded a figure of 6.46, or the IDR for patients greater than 60 years old was 0.96, whereas the RR achieved a significant value of 1.67. This suggests that the use of IDR to analyze risk factors for nosocomial infection improves comparability of results obtained in different hospital settings. Also, it may allow a more exact quantification of an effect. These facts influence implementation of nosocomial infection control measures.