1. Department of Bacteriology1 and
2. Department of Gynecology and Obstetrics, National Hospital,2
3. Department of Microbiology, Ullevål University Hospital,3 and
4. Section of Food Hygiene, Norwegian College of Veterinary Medicine,4 Oslo, Norway, and
5. Institute of Child Health, University of Bristol, Bristol, England5
6. Department of Social Medicine,6 National Institute of Public Health,