1. Foodborne and Diarrheal Diseases Branch, Division of Bacterial and Mycotic Diseases; Centers for Disease Control and Prevention; 1600 Clifton Road Atlanta Georgia 30333
2. General Office of Epidemiology, Ministry of Health; Lima Peru
3. Dirección General de Epidemiologia; Col. Lomas de Plateros Mexico
4. Pan American Health Organization; Washington D.C. 20037