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Electronic letters to:

Research:
Jacques Pépin, Louis Valiquette, and Benoit Cossette
Mortality attributable to nosocomial Clostridium difficile–associated disease during an epidemic caused by a hypervirulent strain in Quebec
CMAJ 2005; 173: 1037-1042 [Abstract] [Full text] [PDF]
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Electronic letters published:

[Read eLetter] Some considerations
Wenbin Liang   (6 October 2005)

Some considerations 6 October 2005
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Wenbin Liang
taking master of public health Curtin University of Technology

Send letter to journal:
Re: Some considerations

wenbin.liang{at}postgrad.curtin.edu.au Wenbin Liang

Dear Editor,

In this study mortality was compared between patients who had exposed to nosocomial CDAD/ described as “cases” and patients who were unexposed/ described as “controls”.[1] Personally, I believe it is a horrible disease, however the results of the study may overestimate the severity of this infection.

The risk of exposing to nosocomial CDAD/ the risk to become a case might be associated with other factors that may affect the mortality. The time when the patients were evaluated using the Charlson Comorbidity Index, was not mentioned in the study. However the infection of interest may happen on patients who were in more serious condition. Therefore to evaluate the baseline characters of the patients in the two groups, it may be best to use the records at the time right before the infection (could be 48 to 72 hours before the diagnosis) to determine the Charlson Comorbidity score (people who evaluate the record could be blinded from the diagnosis). Nevertheless, even if the baseline characters such as Charlson Comorbidity score were evaluated at this time point, there were still residual variation of baseline characters among patients who were evaluated to be the same—there were still some space left for the onset of infection to be associated with poorer baseline condition.

Moreover when the “controls” were chosen, it may be appropriate to blind the person who operated this procedure, from the outcomes of the “controls” in order to avoid the possible selection bias.

Reference

1. Pepin, J., L. Valiquette, and B. Cossette, Mortality attributable to nosocomial Clostridium difficile-associated disease during an epidemic caused by a hypervirulent strain in Quebec. Cmaj, 2005.

Conflict of Interest:

None declared