The Added Value of Post Discharge Surveillance of Surgical Site Infections in a National Mandatory Surveillance System

Background: Surgical site infections (SSIs) lead to increased morbidity and mortality. With the increasing trend towards a reduction in hospital length-of-stay (LOS), post-discharge surveillance (PDS) following surgery is becoming more important.

Objective: To show the importance of post discharge follow-up in determining the true burden of surgical site infections.

Methods: The mandatory Norwegian Surveillance System for Hospital-Acquired Infections (NOIS), implemented by regulation in 2005, requires that all patients included in the system are to be followed up for 30 days after surgery. The Norwegian system is based on the National Nosocomial Infection Surveillance System (NNIS), USA, and the Hospital in Europe Link for Infection Control through Surveillance (HELICS). Surveillance data was collected on all patients who underwent one of five surgical procedures during a 3-month period (September 1st – November 30th) in 2005 through 2008.

Results: During these four years, 90% of all patients in NOIS were completely followed up by the hospitals (endpoint >25 days, organ-space infection or death). The highest follow-up rate was in hip replacement surgery (95%) and the lowest in appendectomy (76%). Of the 895 infections registered in the 14 148 patients with complete follow-up, 757 were diagnosed post-discharge (85%). 20% of these (153/757) were readmitted or had revisional surgery because of their surgical site infection. The mean number of days until infection was 13 (95% CI 12.5-13.6) (median 12), whereas the mean postoperative LOS was 5.7 days (95% CI 5.7-5.8) (median 5 days). During the same four year period, the mean postoperative LOS decreased from 6.2 to 5.5 days (p<0.05) (median 6 to 5 days). National average bed-days data show a similar trend, a reduction from 5.1 to 4.8 days. Over the last 20 years average bed-days decreased from 7.5 to 4.8 in Norway. The overall incidence proportion of surgical site infections (including PDS) was 6.33% and there was no significant reduction in the incidence (p>0,05) over the four-year period. The overall in-hospital incidence was 0.98%, with a significant downward trend (p<0.05) over the four years.

Conclusions: Most surveillance systems do not include mandatory post-discharge surveillance. Across countries post-discharge surveillance is done in a multitude of ways ranging from passive to active and voluntary to mandatory. Post-discharge follow-up is an important, resource demanding and complicated aspect of surveillance of SSI, but necessary in order to obtain a complete picture of morbidity since 85% of infections are detected after discharge from hospital. Passive surveillance, in the form of readmissions and revisions, are not sufficiently detecting the true burden of infections.