OBJECTIVE Sternal wound polymicrobial infections are considered the most dangerous complication of the median sternotomy in cardiothoracic surgery. In addressing this issue, an investigation team consisting of the medical microbiologists, infection control professionals and infectious disease physicians participated in tracking the source and monitoring progression of infection.

METHODS Various types of microbial specimens from the patient and the highly suspicious reservoirs of the infection were collected. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry and metagenomic second generation sequencing were used for microbial identification. Semi-quantitative plate culture technique was used to assess the microbial load at the wound site. Infected wound care involves intravenous antibiotics administration, extensive surgical debridement, negative pressure wound treatment, and irrigation of the wound with silver ions. The rigorous disinfection process with sodium hypochlorite and hydrogen peroxide was performed to decontaminate heater-cooler units used in the cardiac surgery operating room.

RESULTS The investigation of sternal wound microbial profile showed the wound infection evolved from a monomicrobial to a polymicrobial state. The identified pathogens included Mycobacterium farcinogenes, Serratia marcescens, Klebsiella pneumoniae, and Candida parapsilosis. The source of M. farcinogenes associated with post-sternotomy infection was traced to the heater-cooler units used for cardiopulmonary bypass. The periphery skin of the wound was identified with S. marcescens, K. pneumoniae, and C. parapsilosis colonization. The load of pathogens on dressing foams and wound bed constantly decreased in gradient changes after the application of comprehensive interventions to control wound infection. The addition of instilation with silver ions can accelerate eradication of pathogens.

CONCLUSIONS Tracking the source of infection and controlling the microbial load in wounds, as an adjunct to surgical debridement and antibiotic therapy are clinically applicable. Infection control practices for postoperative sternal wound polymicrobial infection deserve further consideration. Strengthening the process management of pre-, intra- and post-operative period of infection control can effectively reduce the risk of surgical site infections.