Blood culture test predicts severity of pneumococcal pneumonia: A discussion with Dr. Catia Cillniz

By John J. Murphy, MDLinx
Published August 24, 2017

Key Takeaways

Researchers in Spain have found a simple way to gauge the severity of pneumococcal pneumonia and predict its outcome. They showed that when the "time to positivity" (TTP) of a blood culture takes less than 9.2 hours, then the patient is likely to have more severe pneumococcal pneumonia outcomes.

A patient whose TTP result indicates worse outcomes can then be given more aggressive treatment, the researchers advised. They reported their results in the journal PLoS One.

"Streptococcus pneumoniae remains the most frequent cause of community-acquired pneumonia (CAP)," the authors wrote, noting that patients with bacteremic pneumonia have a 15% to 26% higher mortality rate than non-bacteremic patients. "The identification of early predictors of worse outcome in patients with bacteremic CAP due to S. pneumoniae is therefore of utmost importance."

Previous research on invasive pneumococcal pneumonia suggested an association between high bacterial load and worse clinical outcomes. So, for this study, the researchers reasoned that because TTP has been inversely associated with blood bacterial load, it could be a marker of more severe disease and a potential early predictor of mortality.

To that end, they analyzed 278 cases of bacteremic pneumococcal pneumonia with corresponding TTP results. They found that patients whose TTP was less than 9.2 hours had a significantly higher risk for invasive mechanical ventilation, longer length of hospital stay, higher in-hospital mortality, and higher 30-day mortality compared with those whose TTP was greater than 9.2 hours.

The researchers concluded that pneumococcal pneumonia patients with early TTP are more severely ill at presentation and have worse outcomes.

In this interview, study author Catia Cillóniz, PhD, postdoctoral researcher in the Pulmonology Department at the Hospital Clinic of Barcelona, explains the clinical significance of early TTP and how doctors can use this information in clinical practice.

MDLinx: This is the first study to investigate TTP in relation to pneumococcal pneumonia in a large, adult cohort. What led you to conduct this particular investigation?

Dr. Cillóniz: The evidence about the association between high bacterial load and worse clinical outcomes in invasive pneumococcal pneumonia suggests that determination of pneumococcal load has a clinical utility. TTP is an easy variable related to pneumococcal bacterial load. So, we decided to investigate this variable in order to find associations with outcomes in our cohort of patients.

MDLinx: What was the main finding of your investigation?

Dr. Cillóniz: Our results support the direct relationship between early TTP with severe presentation and worse outcomes in patients with diagnosis of pneumococcal CAP.

MDLinx: How did you decide what length of time would be considered "early detection" and what length of time would be "late detection?"

Dr. Cillóniz: TTP is defined as the time interval between the start of incubation and the detection of microbial growth in peripheral blood, as documented using an automated monitoring system. We found that 9.2 hours is the optimal cut-off point for TTP in relation to in-hospital mortality.

MDLinx: Why do you think early TTP relates to the severity of pneumococcal bacteremic pneumonia?

Dr. Cillóniz: Early TTP of blood cultures is directly related with a higher bacterial concentration in blood. This is the main reason why early TTP is related to severity in pneumococcal bacteremic pneumonia.

MDLinx: Is TTP easier to obtain than other tests of bacteremic pneumococcal pneumonia?

Dr. Cillóniz: Data about TTP is always available in the microbiology lab. This data is obtained automatically when a blood culture is positive for pneumococcus. However, this data is never reported in the routine clinical practice.

MDLinx: How could physicians use this information in clinical practice?

Dr. Cillóniz: TTP data should be reported routinely in order to help clinicians to identify patients at risk of worse outcomes who could benefit from more aggressive early management.

MDLinx: What is your next step in this line of research?

Dr. Cillóniz: We will continue to investigate the factors related to the host and the pathogen that will help to improve the clinical outcomes in patients with pneumococcal pneumonia.

About Dr. Cillóniz: Catia Cillóniz, PhD, is an Associate Professor of the Faculty of Medicine at University of Barcelona, and a postdoctoral researcher and the coordinator of the Community-Acquired Pneumonia Research Group at the Hospital Clinic of Barcelona, in Barcelona, Spain.

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