An NNIS risk index score was calculated for each patient by assigning one point each for a contaminated wound, an ASA score [is greater than or equal to] 3, and surgical procedures lasting longer than the NNIS-derived 75th percentile for the duration of the procedure (23).
Two variant scores were also computed; in one of these, a chronic disease score [is greater than or equal to] 5,000 was substituted for ASA score [is greater than or equal to] 3, and in the other, a point was added to the NNIS score for a chronic disease score [is greater than or equal to] 5,000.
Other recognized risk factors, such as procedure type and NNIS wound class, were not significantly associated with infection because of the matching procedure that was used to select uninfected controls.
In this population, the NNIS risk index was correlated with infection status (Figure 2A).
The chronic disease score performed comparably with the ASA score as a component of the NNIS risk index, and an NNIS-like index based on both the chronic disease and ASA scores performed better than the conventional NNIS index.