Annual incidence rates of septic arthritis increased significantly in WA between 1990 and 2010 and may continue to do so.
The findings are consistent with most other studies of septic arthritis and have consequences in terms of patient morbidity and mortality and costs such as acute hospital admissions and long-term complications.
The study, using data from the Western Australian Rheumatic Disease Epidemiological Registry, found the rates of septic arthritis increased from 4.39 per 100,000 in 1990 to 12.87 per 100,000 twenty years later.
Knee and wrist joints were the most commonly affected overall though culture positive events were most common in knees and shoulders.
“Staphylococci and streptococci were the main causative agents (62.8%) in cases where microorganisms were identified, but other micro-organism were found in over a third of culture-positive patients,” the study authors from the Department Rheumatology, Sir Charles Gairdner Hospital, Perth, said.
Published in the International Journal of Rheumatic Diseases, the findings showed a rising incidence rate of septic arthritis over time coincided with an increase in age at diagnosis (from 45.1 to 55.6 years) and the proportion of female patients (from 23% to 36%).
The average time spent in hospital for septic arthritis was 5 days with a longer length of stay in culture-positive patients.
Of the culture positive patients, 3.6% required ICU admission, 32.3% required hospital readmission, and 31-day mortality was 6.2%.
“Compared with the general WA population, excess mortality was observed in patients with culture-positive septic arthritis across all age and gender categories, confirming the serious nature of septic arthritis.”
Indigenous Australians were overrepresented in the cases compared to their proportion in the WA population (16.4% v 4%).
Long term complications included osteomyelitis (4.7% in culture positive patients) and osteoarthritis (7.3% in culture positive patients).
“Overall, the use of hospital resources (25 925 subsequent ED visits [median 6, IQR 3-14] and 44 024 admissions [median 7, IQR 3-15]) were substantial,” the study authors said.
Led by Professor Johannes Nossent from the University of Western Australia, the investigators said the reasons behind the rise in septic arthritis cases were not clear but the incidence was likely to continue to rise.
“A contribution from increasing numbers of diagnostic and therapeutic joint procedures has been described, while other studies suggest a role for ageing populations with underlying organ-based comorbidities,” they wrote.
“Our data confirm the role of comorbidity with septic arthritis being the first hospital contact ever in a minority of patients only (10.4%) and 80% of patients having already accrued some comorbidity at septic arthritis diagnosis associated with a high rate of prior serious infections.”
“Importantly, our data show that suspected septic arthritis is not per se a benign condition with a 1% short-term mortality and increased SMRR in the age group 40- 59 years. This supports recommendations that negative or absent microbiology testing in clinically suspected septic arthritis should not deter from initiating therapy.”
Professor Nossent told the limbic that increasing longevity and levels of comorbidity in combination with high levels of medical and surgical interventions was the most likely explanation for increased incidence of septic arthritis.
He said the clinically important messages were that septic arthritis was now seen more often in female patients, the shifting microbiological spectrum included Gram negative organisms, and that a negative culture – which was not infrequent in practice – should not preclude antibiotic therapy when there was otherwise a high clinical suspicion of septic arthritis.