Impact on Morbidity, Mortality, and Length of Stay of Hospital-Acquired Infections by Resistant Microorganisms

スペインの大学病院単施設による、院内耐性菌の感染インパクトをレトロスペクティブに調査したCID論文。

Background

Infections by multidrug-resistant organisms (MDROs) are a global threat and are particularly common in hospitals. This study was performed to assess the impact of hospital-acquired infections caused by MDROs on morbidity, mortality, and length of hospital stay.

Methods

This was a retrospective cohort study. A sample of adults aged ≥18 years with a respiratory, urinary, bloodstream, or surgical site infection caused by a multidrug-resistant (cases) or -sensitive (controls) microorganism was selected. Measurements included hospital mortality from all causes (total and 30 days after infection), length of stay (LOS), and 5 indicators of morbidity: intensive care or surgery admissions, number of diagnostic tests after infection, and hospital readmissions or visits to the emergency department within 30 days of discharge.

Results

The sample was composed of 324 cases and 676 control patients. Risk of hospital mortality from all causes (hazard ratio [HR], 1.7; 95% confidence interval [CI], 1.25–2.32) and 30 day-mortality after infection (HR, 1.77; 95% CI, 1.29–2.44) were higher in patients with an MDRO infection. Probability of readmission was also higher (odds ratio [OR], 2.17; 95% CI, 1.36–3.46) in the case group. Emergency department visits were only significantly higher in methicillin-resistant Staphylococcus aureus (OR, 2.80; 95% CI, 1.65–4.74) and in Escherichia coli–resistant infections (OR, 2.28; 95% CI, 1.32–3.96). Infections by MDRO were not associated with any other outcome.

Conclusions

Hospital infections caused by MDROs increase mortality, readmissions, and in some cases, visits to the emergency department compared with those produced by susceptible strains. They do not appear to influence LOS nor the need for hospital admission, intensive care, surgery, or diagnostic tests.

Total and 30-day in-hospital mortality

The overall in-hospital mortality from all causes was significantly higher (p=0.001) in cases (24.1%) than in controls (15.4%). Mortality was also associated with age, sex, Charlson comorbidity index, McCabe severity scale, onset of infection in the ICU, absence of surgical history, respiratory or bloodstream infections and P. aeruginosa isolation in the etiology of HAI (Table 4).

After adjusting the data using Cox regression, mortality in HAI in which a MRO was involved (HAI-MRO) was 1.7 times higher (HR= 1.7; 95% CI= 1.25 to 2.32) than in infections by susceptible microorganisms. Other factors associated with adjusted risk of mortality were age, male sex, Charlson comorbidity index, McCabe severity scale, onset of HAI in the ICU and BSI (Table 5).

Post-infection LOS

The average post-infection LOS of patients who survived was slightly higher in cases (17.0±17.3) than in controls (15.8± 15.6), although these differences did not have statistical significance (p=0.339).

30-day readmissions

15.9% of patients discharged after a HAI-MRO were readmitted within 30 days, compared to 8.0% of those infected with a sensitive strain (p=0.001) . In the logistic regression model, the exposure increased the probability of readmissions by 2.17 times (OR= 2.17; 95%CI= 1.36 to 3.46).

Other variables associated with a higher probability of readmission were being admitted to different services instead of ICU, having had a HAI not related to UTI, having a score of 2 on McCabe severity scale or a score of 3-4 on Charlson index (Table 6).

Visits to the emergency department within 30 days

28.5% of patients with a HAI- MRO attended the emergency department at least once within 30 days after discharge, compared to 16.1% of those in which a sensitive strain was involved (p=0.000). Nevertheless, after adjustment by logistic regression, MRO exposure as a whole ceased to be a factor associated with a higher probability of emergency department visits, except if they were HAI produced by MRSA (OR= 2.80; 95%CI= 1.65 to 4.74 ) and E. coli resistant (OR = 2.28; 95%CI= 1.32 to 3.96).

Need for surgery, ICU admission or diagnostic tests

HAI-MRO were not associated with an increased frequency of subsequent surgeries (15.4% vs. 15.8%), ICU admissions (6.0% vs. 9.8%; p=0.08), or requests for diagnostic tests (13.6±18.3 vs 11.6±14.8; p=0.08).

Results for each type of microorganism

Table 7 shows the main results for the type of microorganism involved in HAI in those outcome variables that were significant in the general analysis. MRSA showed an increased risk of both in-hospital mortality and 30-day readmissions or emergency department visits. P. aeruginosa CR was only related with mortality and E. coli ESBL with 30-day readmissions and emergency department visits. HAI by K. pneumoniae ESBL did not appear to be associated with an increased risk in any of the outcomes analyzed.

Limitations

First, quality of records might be affected due to the retrospective design.

Second, the attribution of mortality results to exposure could be questionable due to the lack of information on the real causes of death of patients.

Third, we didn’t measure the appropriateness or delay in the antibiotic treatments, important factors that could influence the results.

Fourth, we didn’t consider exposure as a time-dependent variable, which could bias the exposure effect.

Fifth, our study was done from a hospital perspective (other perspectives are needed) and finally, data from a single hospital provide internal validity but don’t ensure external validity.

f:id:akinohanayuki:20170824045810p:plain