INFECTION AFTER PRIMARY TOTAL HIP ARTHROPLASTY: A COMPARISON OF TIME TRENDS IN TWO NATIONAL HEALTH REGISTERS IN NORWAY FROM 2013 TO 2022

Aim Two types of national registers surveil infections after primary total hip arthroplasty (THA) in Norway: The National surveillance system for surgical site infections (NOIS) that surveil all primary THAs 30 days postoperatively for surgical site infections (SSI), and the Norwegian Arthroplasty Register (NAR) that follow all THAs until any surgical reoperation/revision or the death of the patient. Since these registers report on the same THAs we assessed correspondence between and time trends for the two registers in period 2013 to 2022. All reported THAs were included. Method The THAs were matched on a group level according to sex, age and ASA-class. In addition to descriptive statistics, adjusted Cox regression analyses were performed with adjustment for sex, age group (<45, 45-54, 55-64, 65-74, 75-84, >85 years) and ASA-class (1, 2, 3, 4 and missing). Changes in annual incidence and adjusted hazard rate (aHR) was calculated. Endpoints in the NOIS were 30-Days SSI and 30-Days reoperation for SSI. Endpoints in the NAR were 30-Days and 1-Year reoperation for periprosthetic joint infection (PJI). Results The NOIS had registered 87,923 THAs with 1,393 (1.58%) SSIs and 765 (0.87%) reoperations for SSI within 30 postoperatively. The NAR had registered 91,194 THAs with 725 (0.80%) reoperations for infection after 30 days, and 1,019 (1.21%) reoperations for infections after one year. The distribution of sex, age and ASA-class was near identical in the two registers. There was a mean annual reduction in risk of both SSI (aHR 0.92 (95% CI 0.90-0.93)) and reoperation for SSI (0.95(0.92-0.97)) and PJI (30-Days: 0.96 (0.94-0.99), 1-Year: 0.95-0.99)) over the period 2013-2022. Conclusions The NOIS and the NAR have excellent completeness and the registrations in both registers may be considered representative for the Norwegian population. Not all SSI are reoperated. The incidence and risk of SSI (NOIS) and reoperation for PJI (NAR) is declining and may reflect a true reduction in incidence of PJI after primary THA.