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NAP1 strain of C. difficile predicted severe disease, outcome

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March 14, 2014

The North American pulsed-field gel electrophoresis type 1, or NAP1, strain of Clostridium difficile was the most prevalent strain identified from population-based surveillance, CDC researchers reported. The strain also was a predictor of severe disease, severe outcome and death, they found.

“The practical implications of this finding remain to be determined,” the researchers wrote in Clinical Infectious Diseases. “Host-related factors play an important role in the development of CDI, and other studies have suggested that clinical scores or biomarkers based on the immune response of the host, rather than strain type, should be the basis for decisions about severity of disease for treatment.”

The researchers used data from the CDC’s Emerging Infections Program C. difficile surveillance. The study included 2,057 cases from 2009 to 2011 that had strain typing results available. The most common strain type was NAP1, which comprised 28.4% of the cases. Other common strain types included NAP4 (10.2%), NAP11 (9.1%) and NAP6 (6.6%).

Among patients with strain typing, 363 (17.7%) met the criteria for severe disease. NAP1 strain was significantly associated with severe disease (adjusted OR=1.74; 95% CI, 1.36-2.22). One hundred cases (4.9%) also experienced severe outcomes: 41 were admitted to the ICU. Six underwent colectomy and 70 died within 30 days of infection. NAP1 strain also was a predictor of severe outcomes (adjusted OR=1.66; 95% CI, 1.09-2.54). The NAP1 strain was more common among patients who died within 14 days of stool collection (adjusted OR=2.12; 95% CI, 1.22-3.68).

“Our results represent the largest study to date to examine the association between strain type and disease outcomes,” the researchers wrote. “Furthermore, inclusion of cases from a wide geographic spread reduces bias due to regional variation in C. difficile strain type or patient characteristics.”

Disclosure: One researcher reports financial relationships with Actelion, Cubist, Merck, Novartis, Rebiotix, Roche, Sanofi-Pasteur, Summit and ViroPharma.

itj+ Perspective

Herbert L. DuPont

Herbert L. DuPont

This multi-state study shows that NAP1 strains cause a quarter of all cases of CDI and that infection by these strains predicted severe disease and an increased day-14 mortality. While NAP1 strains have previously been shown to produce serious disease and death in outbreak studies in Canada, a more recent report suggested that the NAP1 strains did not contribute to disease severity. Interesting parts of this study are that the NAP1 strains are more common than many of us thought, they contribute to a more serious outcome and most of the NAP1 strain CDI cases were from community sources. Efforts to control use of fluoroquinolones could help in the reduction of infections by NAP1 strains. 

Herbert L. DuPont, MD
Infectious Disease News Editorial Board member

Disclosure: DuPont reports no relevant disclosures