Nonautomated Blood Cultures in a Low-Resource Setting: Optimizing the Timing of Blind Subculture

Abstract

Laboratory procedures for blood cultures in a hospital in Phnom Penh were adapted to optimize detection of Burkholderia pseudomallei, an important pathogen in this setting. The effects of these changes are analyzed in this study. Blood cultures consisted of two BacT/ALERT bottles (bioMérieux, Marcy-l'Etoile, France). Growth was detected visually by daily inspection of the bottles. In 2016, the aerobic-anaerobic pair (FA/FN FAN) was substituted by an aerobic pair of BacT/ALERT FA Plus bottles. Blind subculture (BS) (subculture in the absence of visual growth) was advanced from day 3 to day 2 of incubation in July 2016. In July 2018, it was further advanced to day 1 of incubation. From July 2016 to October 2019, 9,760 blood cultures were sampled. The proportion of cultures showing pathogen growth decreased from 9.6% to 6.8% after the implementation of the laboratory changes (P < 0.001). Advancing the BS from day 3 to day 2 led to an increased proportion of pathogens detected by day 3 (92.8% versus 82.3%; P < 0.001); for B. pseudomallei, this increase was even more remarkable (92.0% versus 18.2%). Blind subculture on day 1 similarly increased the proportion of pathogens detected by day 2 (82.9% versus 69.0% overall, 66.7% versus 10.0% for B. pseudomallei; both P < 0.001). However, after implementation of day 1 subculture, a decrease in recovery of B. pseudomallei was observed (12.4% of all pathogens versus 4.3%; P < 0.001). In conclusion, earlier subculture significantly shortens time to detection and time to actionable results. Some organisms may be missed by performing an early subculture, especially those that grow more slowly.

Biphasic versus monophasic manual blood culture bottles for low-resource settings: an in-vitro study

“…Day 1 blind subculture yield and growth speed were higher than clinical conditions, with studies reporting a 82-85% pathogen recovery rate using day 1 blind subculture, including in low-resource settings. 30,31 This finding could be because we had higher spiked blood bacterial concentrations than what is typically observed in septic patients in health-care settings (<10 CFU/mL) 1 . Moreover, our growth detection was conducted by expert, non-blinded laboratory technicians, so even subtle signs were likely to be interpreted as signs of growth.…”

“…Optimal timing of blind subculture can also differ according to setting. 31 Additionally, plasma substances in septic patients (including antibiotics) inhibit bacterial growth. Patients in low-resource settings might be on empiric antibiotic therapy before they reach the hospital, which can affect BCB yield and growth speed.…”

Comparative evaluation of Panther Fusion and real-time PCR for detection of Burkholderia pseudomallei in spiked human blood

“…The culture-independent nature of this technique could reduce this window period by approximately 24 h in non-blood specimens. In bacteraemic patients molecular identification directly from blood at the time of presentation could decrease time to diagnosis by more than 48 h [10,11].…”