Table 1. Personal characteristics of ill persons and clinical symptoms, tourist resort, Italy, July 2000 Characteristics Information available (n) Age (years); mean (range) Female (%) Diarrhea (%) Vomiting (%) Fever (%) Abdominal pain (%) Hospitalization (%) Guests 179 23 (1–88) 52 93 84 53 63 2.2 Staff members 26 (19–53) 24 (1–88) 69 54 92 72 58 83 1.4 Total 248 53 93 80 54 70 2.0 RESEARCH Analytical Epidemiology For the analysis of risk factors in the cohort study, 181 questionnaires from 224 staff members were completed and analyzed. The attack rate in this group was 69 (38.1%) of 181. The lowest attack rates were observed in staff members who worked in the kitchen or the office, and the highest were in waiters, sports trainers, entertainers, and cleaning staff (i.e., staff members who have close contact with guests) (Table 2). Staff members who took showers on the beach or consumed drinks with ice were more likely to become ill than those who did not. No association was found between disease and eating any particular type of food or with being at work on July 8–11 (the first days of the outbreak) (Table 3). Microbiologic Results Stool samples from 28 patients were negative for ova and parasites and bacterial enteropathogens. Of the 28 stool sam- ples examined by NLV-specific RT-PCR, 22 had an amplified DNA of the size expected for NLV. The 327-bp amplification product was also confirmed for all samples by Southern blot hybridization with NLV-specific probes. Vomit specimens from two other subjects were negative. A readable common sequence of 290 bp was obtained with sequence analysis and found to be the same for eight samples, indicating a single outbreak virus strain. The sequence was analyzed against the European Molecular Biology Laboratory Nucleotide Data Bank, yielding a best fit with the RNA poly- merase sequence of the Lordsdale strain of NLV (16). Nucle- otide identity between the two strains was 93.1% (270/290 residues), indicating that the outbreak NLV strain belongs to GGII. When the stool supernatants stored at -20°C were exam- ined by the Vero cell assay for free bacterial toxins, a CPE consistent with that of C. perfringens enterotoxin was induced by seven samples. The RPLA test confirmed the presence of C. perfringens enterotoxin in all seven samples. The positive specimens had been collected July 18–21, and all were also positive for NLV (Table 4). Figure 3. Cases of gastroenteritis with known date of onset (n=333) in guests and staff members at a tourist resort, Italy, July 2000. >70% of all cases. Five patients were hospitalized; all recov- ered rapidly and were discharged within a few hours. None of the patients had any further sequelae. Attack rates did not dif- fer by age, sex, or symptoms for cases in guests or staff mem- bers. For cases in guests, the median interval from the arrival date at the resort and onset of symptoms was 4 days, and symptoms developed in 77% within 5 days. The epidemic curve shows three distinct peaks in each of the 3 weeks, beginning on July 12 (70 cases), July 18 (26 cases), and July 27 (55 cases). Over the total outbreak period, 275 cases occurred in guests and 58 in staff (Figure 3). Fifty- seven percent of cases in staff members occurred before July 15. The outbreak lasted 24 days, and no cases were observed after July 31. Because of the rapid turnover at the resort, attack rates for guests were calculated separately for each week: an attack rate of 102 (10.5%) of 970 was observed in week 1; 66 (8.7%) of 760 in week 2; and 105 (10.1%) of 1,034 in week 3. Ill guests occupied 157 of the resort’s 456 rooms. No significant evi- dence of either clustering by the cluster k-means methods (p=0.392) or increased frequency of cases in rooms near the water pipeline was observed. Attack rates by sex, age group, and week of stay were similar. Emerging Infectious Diseases • Vol. 8, No. 6, June 2002 565