Data published in JAMA Surgery showed patients with 30-day postoperative infection had a 3.2-fold higher risk for 1-year infection and a 1.9-fold higher risk for mortality compared with those with no infections.
A retrospective observational cohort study recruited veterans undergoing major surgery through the Veterans Health Administration from January 2008 to December 2015. Patients with any 30-day postoperative infection were placed in the exposure group, and those with no infection comprised the control group. The number of days between index surgery and the occurrence of death or the patient’s first infection during postoperative days 31 to 365 was recorded, and patients who died before having a long-term infection were censored for the infection outcome.
The mean age of the 659,486 included patients was 59.7 years (standard deviation, 13.6 years), and 3.6% had a 30-day infection, 6.6% had a long-term infection, and 3.8% died during the follow-up period. Surgical site infections (40.2%), urinary tract infections (27.5%), pneumonia (14.8%), and bloodstream infections (8.0%) were the most frequent 30-day conditions.
Long-term infections included urinary tract infection (48.7%), skin and soft tissue infection (32.6%), bloodstream infection (8.8%), and pneumonia (5.8%). The exposure group had a higher observed incidence of long-term infections (21.8%) and mortality (12.9%) compared with the control group (6.1% and 3.4%, respectively). The estimated hazard ratio for long-term infection was 3.17 (95% CI, 3.05-3.28), and 1.89 (95% CI, 1.79-1.99) for mortality.
Researchers noted that most patients included in the study were men, which is common of most veteran populations, and therefore results may lack external validity for other populations. Investigators also noted that the models used did not account for the likely additional harm of an organ/space surgical site infection relative to a superficial surgical site infection or urinary tract infection. This was done to simplify the assumption of homogeneity of the exposure. It is also possible that long-term infections were undercounted in those cases where patients received treatment outside the VA.
Because of limitations from the data sources and retrospective study design, there were no controls applied for potential postexposure confounders with a causal relationship to long-term infection or mortality. Selection bias for the exposure and unmeasured/unobservable confounders may also be present. Finally, implicit in the Cox proportional hazards model is the assumption that the ratio of hazards in the 2 groups is constant over time, which may not reflect the true relationship. However, investigators believe this risk is minimal.
Investigators concluded that, “the occurrence of a postoperative infection, independent of patient characteristics and surgery factors, is associated with increased likelihood of having a subsequent infection and mortality up to 1 year after the initial surgery.” Patients with 30-day postoperative infection had a 3.2-fold higher risk for 1-year infection and a 1.9-fold higher risk for mortality compared with those with no infections. They further recommended that increased harm and cost of long-term infections should be included in future cost-benefit calculations and prevention initiatives.
O’Brien WJ, Gupta K, Itani KMF. Association of postoperative infection with risk of long-term infection and mortality [published online November 6, 2019]. JAMA Surg. doi:10.1001/jamasurg.2019.4539