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Pneumonia Severity and Bacterial Load
In patients with community-acquired pneumococcal pneumonia, high bacterial load at admission was associated with need for mechanical ventilation, development of shock, and in-hospital death.
During the past decade, we have gained a better understanding of the consequences of immune system activation during bacterial infections, including severe sepsis and shock. In routine clinical practice, the severity of such infections is assessed using clinical parameters alone; the microbiology laboratory contributes information only on the pathogen and its resistance pattern (and does so with considerable delay). Might bacterial load also provide an important clue? To find out, researchers conducted a prospective study involving 353 adults in Spain who were hospitalized with community-acquired pneumonia and had not received antibiotics before admission.
Ninety-three of the patients had evidence of pneumococcal infection. Blood cultures drawn at admission grew pneumococci in 34 of these patients; pneumococcal DNA was detected by quantitative real-time PCR in the blood of 58. Positive PCR results were significantly associated with positive blood cultures, acute renal failure, septic shock, need for mechanical ventilation, and in-hospital mortality. Streptococcus pneumoniae bacterial loads 
1000 copies/mL (seen in 27 patients) were significantly associated with bacteremia (odds ratio, 6.3), acute renal failure (OR, 7.0), acute respiratory distress syndrome (OR, 14.8), need for mechanical ventilation (OR, 10.5), septic shock (OR, 8.0), and in-hospital mortality (OR, 5.4).
Comment: The bacterial load in blood appears to be useful for assessing disease severity in patients with pneumococcal pneumonia. Further refinement and broader availability of such PCR techniques might allow extension of this diagnostic measure to other common pathogens, with the advantage of rapid availability of quantitative results. Eventually, bacterial load might be used as a parameter in sepsis scoring systems.
Published in Journal Watch Infectious Diseases October 7, 2009
Citation(s):
Rello J et al. Severity of pneumococcal pneumonia associated with genomic bacterial load. Chest 2009 Sep; 136:832.
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