Ann Versporten, Ingrid Morales, Carl Suetens 4 th Congress of the International Federation of Infection Control – Malta November 11, 2003 Scientific Institute of Public Health Data validation study of the Belgian national surveillance of nosocomial infections in intensive care units

Background: Belgian National ICU surveillance 1996: Start National Surveillance of ICU acquired infections (Pneumonia & Bacteraemia) –ICU acquired : admitted >48h in ICU –patient-based surveillance: 1 file by patient, + infection file if ICU-acquired PN or BAC

Validation study : main aim Determination of Sensitivity & Specificity of reported ICU-surveillance data (PN & BAC) against a reference gold standard Evaluate the accuracy of all data reported to the surveillance Exhaustiveness (completeness) of the denominator

Methods : sample size Anticipated : Se = 65% ± 5% Sp = 99.5% ± 0.5% Prevalence of 7%  1300 patient charts in a total of 45 hospitals :  268 PN +  128 BAC + (declared BAC on blood culture list)  904 PN – (= 20% of total PN-) Exhaustiveness of denominator : estimation on the base of administrative lists of ICU-admissions

Methods (next) Retrospective patients chart review methodology Research team = “gold standard”  trained data collectors (NSIH team)  application protocol definitions  evaluation = blind  discrepant infections: reviewed by other colleague

Results : Pneumonia (n=33 hosp.) Results from validation study for PN

Results : Bacteraemia (n=33 hosp.) Results from validation study for BAC

Results (ongoing, n=33 hosp.) Se % (95 % CI)Sp % (95% CI) Pneumonia 53,7 (45,4-61,9)98,5 (97,7-99,1) Bacteraemia 60,9 (44,5-75,4)99,4 (98,2-99,7) Exhaustiveness of denominators : 81,2% for all patients staying >48h in ICU

Discussion PN & BAC : low Se., good Sp. 50% of the collected data concern the 3 first surveillance quarters that hospitals participated to our ICU surveillance Exhaustiveness denominator: improvement possible

Who are those missed patients ?? Why are there so many false negative Pneumonias ?

Characteristics false negative PN Pneumonia N % mort. P< Mean LOS (days) P< Mean ventilation (days) P< True + PN False - PN True - PN

Characteristics false negative PN (next) PneumoniaN Median PN Risk score P< % without micro-org. P< Mean post infect. (days) NS True + PN False - PN True - PN

Factors influencing the Se. & Sp. of the infection data Who collects data ? Who decides whether a PN should be reported or not ? Criteria used for blood culture? Adherence to protocol definitions Degree of workload (ratio patient/staff) Size of hospital …

Conclusions Exhaustiveness varies by hospital, but remains satisfactory in general BAC more accurately reported than PN (Se) Seldomly infections reported which were not a nosocomial infection (Sp)  half of FP were infections at entry (47%) Absence of a gold standard !  problem for diagnostic of PN, certainly those without identification of a micro-org.

What have we learnt ? Improve Sensitivity –Improve case finding by  Good communication and training data collectors at hospital level  Importance of electronic surveillance  Surveillance = a standardised tool to measure nosocomial infections Surveillance = not an audit