Characteristics of the subjects
2437 patients with HAIs and 38555 patients without HAIs were enrolled in the present study (Figure. S2). The prevalence of HAIs among the patients was 5.9%. 2363 patients had HAIs at one site, 74 patients had two or more sites. Among 2512 HAIs, the most common HAIs were SSI (n=1511), followed by VAP (n=520), CRBSI (n=319), and CATUIS (n=162), respectively. Patients with HAIs were matched with patients without HAIs at a 1:1 ratio and 2437 patients without HAIs were selected. Baseline characteristics of patients were presented in Table 1 according to the development of HAIs or not. No significant differences were observed in age, gender, and invasive interventions between cases and controls. Other variables were also compared between the two groups. Significant differences were found in ethnicity, renal failure, liver disease, obesity, blood transfusion, and TPN between patients with HAIs and without HAIs (Table. 1).
Outcomes of patients with or without HAIs
As shown in Table 1, when compared with patients without HAIs, those who developed an infection had a longer ICU length of stay (4.24 days [IQR 1.99-11.75] vs 2.66 days [IQR 1.47-5.09], P<0.001) and hospital length of stay (16.06 days [IQR 9.22-26.84] vs 7.97 days [IQR 5.29-13.73], P<0.001). Additionally, although there was no significant difference in 30-day crude mortality between patients with and without HAIs (309 deaths [12.7%] vs 287 deaths [11.5%], P=0.219), and the crude mortality of patients with HAIs were higher than those without HAIs at 60-day (432deaths [17.7%] vs 353 deaths [14.5%], P=0.002), 90-day (509 deaths [20.9%] vs 394 deaths [16.2%], P<0.001) and 1-year (756 deaths [31.0%] vs 573 deaths [23.5%], P<0.001) (Table. 1).
As shown in Table 2, after adjusting for ethnicity, chronic comorbidity (renal failure, liver diseases and obesity) and interventions (blood transfusion and TPN), there was no significant difference in 30-day mortality (OR 1.14, CI95 0.96-1.35, P=0.15) between patients with HAIs and those without HAIs (Table. 2). Significant differences in 60-day, 90-day, and 1-year mortality were noted between the two groups, and the adjusted ORs were 1.29 (CI95 1.11-1.51, P=0.001), 1.39 (CI95 1.20-1.61, P<0.001), and 1.46(CI95 1.29-1.66, P<0.001), respectively (Table. 2).
Relationship between admission SIRS score and HAIs
Table 3 shows that the incidences of HAIs in SIRS score 0 to 4 groups were 31.9%, 40.9%, 46.6%, 50.1%, and 54.7%, respectively. The incidence of HAIs in patients with SIRS (score≥2) was higher than that in patients without SIRS (50.9% vs. 39.8%, P<0.001). The crude ORs for HAIs of SIRS score 1 to 4 on admission were 1.46 (CI95 0.77-2.83, P=0.241), 1.86 (CI95 0.99-3.47, P=0.052), 2.14 (CI95 1.15-3.98, P=0.016), and 2.60 (CI95 1.39-4.80, P=0.003), respectively. The crude OR for HAIs of SIRS was 1.57 (CI95 1.27-1.94, P<0.001) (Table. 3). After adjusting for ethnicity, chronic comorbidity (renal failure, liver diseases and obesity) and interventions (blood transfusion and TPN), ORs for HAIs of SIRS score 1 to 4 on admission were 1.48 (CI950.77-2.83, P=0.232), 1.858 (CI95 0.99-3.47, P=0.051), 2.142 (CI95 1.15-3.98, P<0.001), and 2.58 (CI951.39-4.80, P<0.001), respectively (Table. 3 and Figure. 1). Adjusted OR for HAIs of SIRS on admission was 1.57 (CI951.27-1.94, P<0.001) (Table. 3 and Figure. 1).
Association between infectious SIRS on admission and HAIs
The number of patients with definite, probable, possible, and none infection likelihoods on admission were 628 (12.9%), 189 (3.9%), 1103 (22.6%), and 2954 (60.6%) respectively (Table. S1). There were 778 SIRS with definite and probable infectious diseases. The incidence of HAIs in patients with infectious SIRS was 62.2%. The crude OR for HAIs of infectious SIRS was 1.81 (CI951.54-2.11, P<0.001) (Table. 3 and Figure. 3). Additionally, after adjusting for ethnicity, chronic comorbidity (renal failure, liver diseases and obesity) and interventions (blood transfusion and TPN), OR for HAIs of infectious SIRS was 1.78 (CI951.52-2.09, P<0.001) (Table. 3 and Figure. 1).
Subgroup analyses
As shown in Table S1 and Figure 2, when only patients with definite infection likelihood on admission were included in the analysis, the OR for HAIs of SIRS was 1.04 (CI95 0.50-2.15, P=0.914). When the analysis was restricted to only patients with definite and probable infection likelihood on admission, the OR for HAIs of SIRS was 1.32 (CI95 0.68-2.56, P=0.417). When only patients without definite infection likelihood on admission were included, the OR for HAIs of SIRS was 1.61 (CI95 1.28-2.01, P<0.001). When only patients without definite and probable infection on admission were included, the OR for HAIs of SIRS was 1.54 (CI95 1.28-1.93, P<0.001).
Subgroup analyses were also conducted according to admission variables including ethnicity and chronic comorbidity. It was shown that SIRS on admission was not the risk factor for HAIs in non-white patients, and in patients with liver disease or obesity (all P>0.05) (Table. S1 and Figure. 3). In addition, the results revealed that infectious SIRS on admission was not the risk factor for HAIs in black patients and in patients with obesity (all P>0.05) (Table. S1 and Figure. 3).