Acute Bacterial Arthritis: How Long Should You Wait for Culture Results?

Percy Guanzon Balderia, MD; Sherry Pomerantz, PhD; Robert Fischer, MD


J Clin Rheumatol. 2015;21(4):196-198. 

In This Article

Abstract and Introduction


Background: The optimal incubation period for synovial fluid cultures is unknown.

Objectives: Our study was designed to determine the positivity rate and time to positivity of synovial fluid cultures from adults with suspected acute bacterial arthritis.

Methods: We reviewed the charts of 94 adults who had acute monoarthritis. Patients were classified as low risk or high risk for acute bacterial arthritis. The positivity rate and time to positivity of synovial fluid in combined agar plate and broth culture were calculated.

Results: The overall positivity rate was 22.3% (21 of 94). None of the 21 low-risk patients had a positive culture. Twenty-one (28.7%) of 73 high-risk subjects showed growth, with a mean time to positivity of 36.7 ± 27.1 hours. While half of these turned positive within a day of incubation, growth was detected at up to 90 hours.

Conclusions: In patients with acute monoarthritis, especially those at high risk for infection, it is reasonable to incubate cultures for 4 days before considering them to be negative.


Patients with acute joint swelling, erythema, warmth, and restriction of movement should be regarded as having acute bacterial arthritis until proven otherwise.[1,2] Prompt therapy is important as failure to initiate appropriate antibiotics within the first 24 to 48 hours can result in subchondral bone loss and permanent joint dysfunction.[2] However, it may be just as important to discontinue antibiotics early in patients who are unlikely to have an infection as this may prevent the emergence of resistant organisms.[3,4]

A positive synovial fluid culture establishes the diagnosis of acute bacterial arthritis. On the other hand, while a negative result does not exclude the diagnosis, it may affect clinical decision making when the synovial fluid characteristics fall between the traditional criteria for inflammatory and infectious arthritis.

Synovial fluid is routinely incubated for 3 to 5 days, with clinicians typically using the results within 48 to 72 hours in making treatment decisions. However, the optimal incubation period is still unknown.