Time to Positivity Facilitates an Early Differential Diagnosis of Candida tropicalis from Other Candida species

Abstract

Background

Candidemia caused by Candida tropicalis has more serious adverse consequences and an even higher mortality. Time to positivity (TTP) has been widely used to identify microbial species, resistant microorganisms and distinguish real pathogens and pollutants. However, few studies have demonstrated TTP as a presumptive diagnosis of C. tropicalis in patients with candidemia.

Patients and Methods

A retrospective study of 136 episodes of candidemia and simulated blood cultures with 314 episodes of confirmed Candida strains were applied to explore the role of TTPs in diagnosing C. tropicalis. TTPs were recorded as the shorter one if both aerobic and anaerobic vials were positive. Lastly, relationships were tested between TTPs and resistance and initial inocula concentration.

Results

For the retrospective study, the mean of TTPs for C. tropicalis from 136 patients with candidemia was significantly shorter than other Candida species. The area under the receiver operating characteristics (ROC) curve was 0.8896 ± 0.030 with a sensitivity of 92.86% and a specificity of 77.87%, respectively, indicating TTPs with a cut-off value of <25.50 h had a strong diagnostic power for C. tropicalis in patients with candidemia. Moreover, TTPs from 314 simulated blood cultures showed similar results as the retrospective study, demonstrating TTP is a powerful diagnostic tool in early diagnosing C. tropicalis in patients with candidemia. Additionally, our results showed no statistical significance between TTPs and initial inocula concentration and resistance of Candida species, suggesting initial inocula concentration does not impact TTPs, and TTPs may not be promising in predicting the resistance of all Candida species.

Conclusion

TTP can be employed to early distinguish C. tropicalis from other Candida species in patients with candidemia, which is extremely helpful to initiate empiric antifungal treatments to improve clinical outcomes.

Keywords:

• time to positivity
• C. tropicalis
• presumptive diagnosis
• Candida species
• candidemia

Ethics Approval and Consent to Participate

Protocols of human tests (clinical samples) and microbiological research were approved by the Scientific Research Ethics Committee of the Institutional Review Board (IRB) of Clinical Medical College and the First Affiliated Hospital of Chengdu Medical College. We have confirmed that all methods were performed in accordance with the relevant guidelines and regulations. For the collection of clinical isolates, written informed consent was conducted in accordance with the Declaration of Helsinki, and sufficient time was provided for questions and answers before signing written informed consent.

Author Contributions

All authors made a significant contribution to the manuscript, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.

Additional information

Funding

This study was supported by the National Natural Science Foundation of China (81802072) and the First Affiliated Hospital of Chengdu Medical College Program (CYFY2018YB03).