RE: "DO MEN HAVE A HIGHER CASE FATALITY RATE OF SEVERE ACUTE RESPIRATORY SYNDROME THAN WOMEN DO?"

William Goggins

Centre for Epidemiology and Biostatistics, Chinese University of Hong Kong, Shatin, Hong Kong

In a recent issue of the Journal, Karlberg et al. (1) reported on an analysis of severe acute respiratory syndrome (SARS) data from Hong Kong. The authors found a substantial and statistically significantly higher mortality rate for males than for females, which persisted after adjustment for patient age. We wish to report the results of an analysis of similar data from the Taiwan Center for Disease Control (2). After reclassification of the data by World Health Organization case definition and after polymerase chain reaction and SARS antibody testing, the total number of SARS cases in Taiwan during last year’s epidemic was 346; 73 (21.1 percent) of these patients died, either directly from SARS or from a SARS-related cause (2). The overall mortality rate was higher than that reported for Hong Kong (17.0 percent) (1), and the difference was close to significance (p = 0.079). While it was not possible to directly compare the age distributions of the Hong Kong and Taiwanese patients because of differences in the way patients were grouped by age, the distributions appeared to be roughly similar. In addition, since larger percentages of Taiwanese patients were women (63.0 percent vs. 55.8 percent for Hong Kong) and health-care workers (30.3 percent vs. 21.9 percent for Hong Kong), this higher mortality rate could not have been due to confounding by these variables.

Table 1 shows the distributions of cases and deaths by gender and age group. The 128 Taiwanese male SARS patients had a significantly (p = 0.002) higher mortality rate (30.5 percent) than the 218 female patients (15.6 percent). As in Hong Kong, Taiwanese female patients were significantly (p < 0.0005) younger than males, with 55.0 percent of females versus 37.5 percent of males being under 40 years of age at diagnosis, while 25.0 percent of males versus 10.6 percent of females were over age 60 years.


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TABLE 1. Distribution of severe acute respiratory syndrome cases and deaths in Taiwan, by gender and age group, 2003
 
A logistic regression model was fitted to these data with gender and age (imputed as the midpoint of the age interval to which the patient belonged) used as independent variables. While older age remained a significant (p < 0.0005) predictor of mortality, gender was no longer significant (p = 0.178). However, the effect size observed for gender (approximate (3) adjusted relative risk = 1.40, 95 percent confidence interval: 0.74, 2.54) was reasonably close to that estimated for Hong Kong (relative risk = 1.62) (1). Unlike in Hong Kong, the gender difference in mortality did not diminish with increasing age. In fact, the mortality rates were similar for patients under age 40 years at diagnosis (7.5 percent for females vs. 6.3 percent for males) and patients aged 60 years or over (56.5 percent for females vs. 62.5 percent for males); a large mortality rate difference was observed only for patients aged 40–59 years (33.3 percent for males vs. 16.0 percent for females).

The 105 Taiwanese SARS patients who were health-care workers had a mortality rate (11.4 percent) that was significantly (p = 0.0056) lower than that of non-health-care workers (25.3 percent) (2). Given the excess of female SARS patients in the age group 20–49 years, it is likely that most of the health-care workers were young women, as was the case for Hong Kong (1). Therefore, the possibility that health-care-worker status is a confounder of the observed gender-mortality relation cannot be excluded. Likewise, confounding by other variables such as comorbid conditions, smoking history, or time from the appearance of symptoms to hospitalization cannot be ruled out.

Editor’s note: In accordance with Journal policy, Dr. Karlberg and his colleagues were asked whether they wished to respond to this letter, but they chose not to do so.

REFERENCES

  1. Karlberg J, Chong DSY, Lai WYY. Do men have a higher case fatality rate of severe acute respiratory syndrome than women do? Am J Epidemiol 2004;159:229–31.[Abstract/Free Full Text]
  2. SARS (Severe Acute Respiratory Syndrome) Online Information Center, Center for Disease Control, Taiwan Department of Health. SARS data analysis—Taiwan. Taipei, Taiwan: Center for Disease Control, 2004. (World Wide Web URL: www.cdc.gov.tw/sarsen). (Last accessed April 23, 2004).
  3. Zhang J, Yu KF. What’s the relative risk? A method for correcting the odds ratio in cohort studies of common outcomes. JAMA 1998;280:1690–1.[Abstract/Free Full Text]




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