Evaluation of blood culture bottles seeded with X-V factors for the detection of Neisseria meningitidis and Haemophilus influenzae

Time-to-detection of bacteria and yeast with the BACTEC FX versus BacT/Alert Virtuo blood culture systems

BACKGROUND

Bloodstream infections are associated with high rates of morbidity and mortality. Rapid detection of bloodstream infections is important in achieving better patient outcomes.

OBJECTIVE

Compare the time-to-detection (TTD) of the new BacT/Alert Virtuo and the BACTEC FX automated blood culture systems.

DESIGN

Prospective simulated comparison of two instruments using seeded samples.

SETTING

Medical microbiology laboratory.

METHODS

Blood culture bottles were seeded in triplicate with each of the standard ATCC strains of aerobes, anaerobes and yeast. TTD was calculated as the length of time from the beginning of culture incubation to the detection of bacterial growth.

MAIN OUTCOME MEASURES

TTD for the various tested organisms on the two microbial detection systems.

RESULTS

The 99 bottles of seeded blood cultures incubated in each of the blood culture systems included 21 anaerobic, 39 aerobic and 39 pediatric bottles. The BacT/Alert Virtuo system exhibited significantly shorter TTD for 72.7 % of the tested organisms compared to BACTEC FX system with a median difference in mean TTD of 2.1 hours (interquartile range: 1.5-3.5 hours). The BACTEC FX system was faster in 15.2% (5/33) of microorganisms, with a median difference in mean TTD of 25.9 hours (IQR: 9.1-29.2 hours).

CONCLUSION

TTD was significantly shorter for most of the microorganisms tested on the new BacT/Alert Virtuo system compared to the BACTEC FX system.

LIMITATIONS

Use of simulated cultures to assess TTD may not precisely represent clinical blood cultures.

CONFLICT OF INTEREST

None.

Detection of Streptococcus pneumoniae and Haemophilus influenzae type B by real-time PCR from dried blood spot samples among children with pneumonia: a useful approach for developing countries

Background

Dried blood spot (DBS) is a reliable blood collection method for storing samples at room temperature and easily transporting them. We have previously validated a Real-Time PCR for detection of Streptococcus pneumoniae in DBS. The objective of this study was to apply this methodology for the diagnosis of S. pneumoniae and Haemophilus influenzae b (Hib) in DBS samples of children with pneumonia admitted to two hospitals in Mozambique and Morocco.

Methods

Ply and wzg genes of S. pneumoniae and bexA gene of Hib, were used as targets of Real-Time PCR. 329 DBS samples of children hospitalized with clinical diagnosis of pneumonia were tested.

Results

Real-Time PCR in DBS allowed for a significant increase in microbiological diagnosis of S. pneumoniae and Hib. When performing blood bacterial culture, only ten isolates of S. pneumoniae and none of Hib were detected (3·0% positivity rate, IC95% 1·4-5·5%). Real-Time PCR from DBS samples increased the detection yield by 4x fold, as 30 S. pneumoniae and 11 Hib cases were detected (12·4% positivity rate, IC95% 9·0-16·5%; P<0·001).

Conclusion

Real-Time PCR applied in DBS may be a valuable tool for improving diagnosis and surveillance of pneumonia caused by S. pneumoniae or Hib in developing countries.