“Time to Infection Positivity” per Specific Microbe

A first-of-its-kind study of microbial infection has just been published in the Journal of Bone and Joint Surgery (JBJS) by the renowned research team at Philadelphia’s Rothman Orthopaedic Institute.

This novel study collected data regarding “time to positivity”—the interval from the beginning of incubation to the time of the first hint of a microbe. The Rothman Orthopaedic Institute at Thomas Jefferson University Hospital’s research team posited that the time to positivity on culture would vary significantly among different microbial species, as well as among different specimen types.

The results of this teams’ work, “Time to Positivity of Cultures Obtained for Periprosthetic Joint Infection,” was published in the November 18, 2022, edition of JBJS.

The Rothman team along with colleagues in Italy and Germany designed a retrospective study using institutional periprosthetic joint infection databases to identify patients who’d been treated with hip or knee revision arthroplasty from 2017 to 2021. The researchers only included patients who met the 2018 International Consensus Meeting criteria for periprosthetic joint infection and had a positive intraoperative culture.

The team enrolled 536 patients with positive cultures. The median time to positivity for all patients in the study with positive cultures was 3.3 days.

Overall, gram-negative organisms (time to positivity, 1.99 days [1.1 to 4.1]; n = 225) grew significantly faster on culture compared with gram-positive organisms (time to positivity, 3.33 days [1.9 to 5.8]; n = 1,774).

• Methicillin-resistant Staphylococcus aureus (time to positivity, 1.42 days [1.0 to 2.8]; n = 85) had the fastest time to positivity, followed by
• Gram-negative rods (time to positivity, 1.92 days [1.0 to 3.9]; n = 163),
• Methicillin-sensitive Staphylococcus aureus (time to positivity, 1.95 days [1.1 to 3.3] n = 393),
• Streptococcus species (time to positivity, 2.92 days [1.2 to 4.3]; n = 230),
• Staphylococcus epidermidis (time to positivity, 4.20 days [2.4 to 5.5]; n = 555),
• Candida species (time to positivity, 5.30 days [3.1 to 10]; n = 63), and
• Cutibacterium acnes (time to positivity, 6.97 days [5.9 to 8.2]; n = 197).

As for the median time to positivity according to specimen type:

• Synovial fluid (time to positivity, 1.97 days [1.1 to 3.1]; n = 112) had the shortest time to positivity, followed by
• Soft tissue (time to positivity, 3.17 days [1.4 to 5.3]; n = 1,199) and
• Bone (time to positivity, 4.16 days [2.3 to 5.9]; n = 782).

Co-author Saad Tarabichi, M.D., a postdoctoral research fellow at the Rothman Orthopaedic Institute, told OTW, “Antibiotic resistant organisms, such as methicillin-resistant Staphylococcus aureus and gram-negative rods, demonstrated the fastest time to positivity on culture. Although the present study did not demonstrate a correlation between time to positivity and treatment failure, it is well-established that the aforementioned organisms are independent risk factors for treatment failure in patients with periprosthetic joint infection. Furthermore, based on the findings of the present study, it is evident that holding cultures for 14 days is sufficient to capture the majority of causative organisms in the setting of periprosthetic joint infection.”

“Increased awareness of data on time to positivity in this setting may help guide the selection of appropriate antimicrobial therapy and predict treatment outcomes in the future. A limitation of this study is that we were not able to determine whether time to positivity on culture predicted treatment outcomes in patients with periprosthetic joint infection. Future studies are needed in order to determine the role that time to positivity may play in this setting.”