Epidemiology and Infection

Prolonged outbreak of giardiasis with two modes of transmission

D. E. KATZ a1c1, D. HEISEY-GROVE a2, M. BEACH a3, R. C. DICKER a1 and B. T. MATYAS a2
a1 Epidemic Intelligence Service, Office of Workforce and Career Development, Centers for Disease Control and Prevention, Atlanta, GA, USA
a2 Bureau of Communicable Disease Control, Massachusetts Department of Public Health, MA, USA
a3 Division of Parasitic Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA

Article author query
katz de   [PubMed][Google Scholar] 
heisey-grove d   [PubMed][Google Scholar] 
beach m   [PubMed][Google Scholar] 
dicker rc   [PubMed][Google Scholar] 
matyas bt   [PubMed][Google Scholar] 


Large outbreaks of giardiasis caused by person-to-person transmission, or a combination of transmission routes, have not previously been reported. A large, prolonged giardiasis outbreak affected families belonging to a country club in a suburb of Boston, Massachusetts, during June–December 2003. We conducted a retrospective cohort study to determine the source of this outbreak. Giardiasis-compatible illness was experienced by 149 (25%) respondents to a questionnaire, and was laboratory confirmed in 97 (65%) of these cases. Of the 30 primary cases, exposure to the children's pool at the country club was significantly associated with illness (risk ratio 3·3, 95% confidence interval 1·7–6·5). In addition, 105 secondary cases probably resulted from person-to-person spread; 14 cases did not report an onset date. This outbreak illustrates the potential for Giardia to spread through multiple modes of transmission, with a common-source outbreak caused by exposure to a contaminated water source resulting in subsequent prolonged propagation through person-to-person transmission in the community. This capacity for a common-source outbreak to continue propagation through secondary person-to-person spread has been reported with Shigella and Cryptosporidium and may also be a feature of other enteric pathogens having low infectious doses.

(Accepted November 16 2005)
(Published Online March 29 2006)

c1 Massachusetts Department of Public Health, 305 South Street, Room 508, Jamaica Plain, MA 02130, USA. (Email: davidkatz1@yahoo.com)