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From 1995 to 1997, we prospectively evaluated the prevalence of hepatitis C virus (HCV) RNA in 124 patients with porphyria cutanea tarda (PCT) from Northern France (83 sporadic and 41 familial PCT). Serum samples were analyzed for ferritin, transaminases, HCV antibodies, and HCV RNA. In addition, genotyping of HCV and searches for HCV infection risk factors (blood transfusion, iv drug abuse, and surgical intervention) were performed. Twentysix of 124 patients (21%; 95% CI: 13.9-28) were positive for serum HCV antibodies. All of them were also positive for HCV RNA. The prevalence of HCV infection was higher in the sporadic PCT group (26.5%, 22 out of 83) than in the familial PCT group (9.7%, 4 out of 41). Risk factors for hepatitis C infection were found to be significantly increased in the HCV-positive group when compared with the HCV-negative PCT group. In all HCV-positive patients with a risk factor, the suspected date of exposure to the virus always preceded the clinical onset of PCT. The HCV genotype pattern in PCT patients was similar to that observed in nonporphyric HCV patients in western European countries. Serum ferritin level was increased in both HCV-positive and HCV-negative porphyric patients. Transaminase levels were significantly higher in HCV-infected PCT patients. Sixty-seven out of 124 patients were retrospectively studied for hepatitis G virus (HGV) infection. Six of these 67 patients (8.9%; 95% CI: 2.1-15.8) were positive for HGV RNA. None of the six HGV-infected patients were positive for HCV RNA. The HGV-infected patients did not differ statistically from those without HGV infection with regard to age, ferritin, transaminase levels, and PCT treatment. These results support the view that sporadic cases of HGV infection may occur frequently. This study of a large cohort of HCV and PCT patients further documents an increasing gradient in HCV prevalence from northern to southern Europe, and shows that HCV infection acts as a triggering factor of PCT. Finally, the HGV prevalence found in the PCT patients was comparable with that found in French blood donors, suggesting that HGV is not a PCT triggering factor. (HEPATOLOGY 1998;27:848-852.)

To the Editor: We believe that Rao et al. might have overstated the accuracy of CT in the diagnosis of appendicitis, which they reported as 98 percent. According to Table 1 of their article, 20 percent of the patients enrolled in the study had symptoms for five or more days. Pain caused by appendicitis that lasts longer than 36 hours often results in perforation 1 ; in one series, a delay of 72 hours or more from the onset of symptoms to surgery resulted in a 90 percent incidence of perforation.2 It seems clear that in patients who have had symptoms for five days or more, the results of abdominal CT will be either impressively positive for appendicitis and its complications or negative. Findings of this nature may thus have led to an increase in the number of either true positive results or true negative results. We would have preferred to see thisThe New England Journal of Medicine Downloaded from nejm.org on May 10, 2018. For personal use only. No other uses without permission.Copyright © 1998 Massachusetts Medical Society. All rights reserved. · June 18, 19 98The New Eng land Jour nal of Medicine study performed in patients who had had symptoms for less than 24 hours. These are the patients in whom the likelihood of missing the diagnosis is highest. To the Editor: In the series of patients evaluated by Rao et al., CT had excellent specificity and sensitivity, as shown by the nearly perfect 90-degree receiver-operating-characteristic curve shown in Figure 3 of the article. However, the curve representing the accuracy of clinical diagnosis makes it look worse than it actually was. According to Table 3, 18 of the 53 confirmed cases of appendicitis (34 percent) and 5 of the 47 cases in which it was ruled out (11 percent) were rated as "definitely appendicitis" by the clinicians. Thus, the first point on the curve should have been plotted at the intersection of 0.11 and 0.34, considerably to the left of the clinical-likelihood curve in Figure 3.Furthermore, the curve for the radiologic likelihood includes patients categorized as definitely not having appendicitis, whereas patients categorized clinically as definitely not having appendicitis were not included in the study. Including these patients, who presumably were correctly classified clinically as not having appendicitis, would shift the curve for clinical likelihood farther to the left. Although the data do suggest that the use of helical CT is promising as an aid to the diagnosis of appendicitis, the study design does not permit direct comparison between CT and clinical examination.University of California, San Francisco San Francisco, CA 94143 Dr. Rao replies:To the Editor: Andersson et al. state that clinical accuracy would have increased after a short period of observation. This may be true, but a delay in diagnosis can be detrimental and costly for patients, whether they occupy emergency department bays or hospital beds.1 On the basis of clinical findings, patients were divided into an observation group (55 patients) and an urgent-appendectomy group ...

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