John Bartlett's Game Changers in Infectious Disease: 2011

John G. Bartlett, MD


October 26, 2011

In This Article

Rapid Microbial Detection

In a study by Bauer and colleagues,[20] molecular techniques were used to rapidly detect MRSA in blood cultures. The outcomes of management of S aureus bacteremia in 2008, predating the use of polymerase chain reaction (PCR) technology at this hospital, were compared with those in 2009, after PCR was implemented. The results are summarized in Table 2, which indicates incredible differences in length of stay and cost.

Table 2. Rapid Detection of MRSA in Blood Cultures

Variable Before PCR After PCR Difference
Length of stay (median) 22 days 15 days -6.2 days
Cost (mean) $69,737 $48,350 -$21,387

Data from Harbath et al.[18]

Why Is This a Game Changer?

In most clinical labs, microbiology is performed the way Louis Pasteur did it in 1850. Specimens are cultured on seaweed and incubated and, 24-48 hours later, whatever has grown is identified. This system seems primitive compared with the modern chemistry laboratory. Chemistry methods are fast, smart, simple, and highly accurate compared with previous methods that were time consuming, complicated, or simply not available.

The introduction of molecular methods for microbial detection represents a quantum leap into the 21st century, having bypassed the 20th century almost completely. Perhaps the best example of use of this technology is the rapid detection of Mycobacterium tuberculosis, which permits conclusions about diagnosis and treatment of tuberculosis (the second most common infectious disease cause of death on earth) in less than 2 hours compared with standard techniques that generally require 4-6 weeks.[21]

In their editorial comment, Small and Pai rightfully referred to rapid detection technology as a "game changer."[22] I selected the Ohio State report because it is probably more relevant to Medscape readers and represents the rational use of this technology in daily practice. Nevertheless, it should be acknowledged that hundreds of similar reports deal with the sudden surge of new opportunities for microbial detection. More importantly, rapid detection promotes optimal antibiotic use in the face of concerns about resistance, abuse, toxicity, and cost.

What Does This Mean to the Practitioner?

PCR technology can be applied to virtually all living microbes, but caution is needed because the methods are incredibly sensitive and specific, to their advantage as well as their disadvantage. Detection of S pneumoniae is useful in the diagnosis of pneumococcal pneumonia if it is from a normally sterile source (empyema or blood), but it is not useful in sputum except to exclude this pathogen or unless quantitation is used. The problem is the high rate of asymptomatic carriage and false positive results.[23]

This technology is readily available for rapid detection of most respiratory tract viral pathogens, but we are now learning that about 15% of healthy adults harbor a respiratory viral pathogen (but not influenza) despite apparent good health.[24] Thus, particular attention needs to be paid to the recovered pathogen, the specimen source, and the "background noise." Examples of optimal use of rapid detection technology are ocular specimens for detecting Herpes simplex, Chlamydia trachomatis, Varicellazoster, Acanthamoeba, and Toxoplasma[25] and respiratory specimens for the detection of pathogens that should never be present in the airways, such as Legionella, C pneumoniae, tuberculosis, influenza, or M pneumoniae.[23]