Risk Factors for Sporadic Giardiasis: A Case-Control Study in Southwestern England

James M. Stuart, Hilary J. Orr, Fiona G. Warburton, Suganthiny Jeyakanth, Carolyn Pugh, Ian Morris, Joyshri Sarangi, Gordon Nichols


Emerging Infectious Diseases. 2003;9(2) 

In This Article

Abstract and Introduction

To investigate risk factors for sporadic infection with Giardia lamblia acquired in the United Kingdom, we conducted a matched case-control study in southwest England in 1998 and 1999. Response rates to a postal questionnaire were 84% (232/276) for cases and 69% (574/828) for controls. In multivariable analysis, swallowing water while swimming (p<0.0001, odds ratio [OR] 6.2, 95% confidence intervals [CI] 2.3 to 16.6), recreational fresh water contact (p=0.001, OR 5.5, 95% CI 1.9 to 15.9), drinking treated tap water (p<0.0001, OR 1.3, 95% CI 1.1 to 1.5 for each additional glass per day), and eating lettuce (p=0.01, OR 2.2, 95% CI 1.2 to 4.3) had positive and independent associations with infection. Although case-control studies are prone to bias and the risk of Giardia infection is minimized by water treatment processes, the possibility that treated tap water is a source of sporadic giardiasis warrants further investigation.

Giardia lamblia, a flagellate waterborne protozoan parasite, is a common cause of gastrointestinal disease in industrialized and unindustrialized countries.[1] Most information on risk factors for giardiasis has come from investigation of outbreaks. Water is the most frequently identified route of transmission,[1,2] through drinking contaminated tap water[3,4] or recreational exposure in lakes, rivers, or swimming pools.[5] Person-to-person spread is well documented in day-care centers and among male homosexuals,[6,7] and food may also be a vehicle of infection.[8]

The relative contribution of these routes of transmission to sporadic cases of giardiasis is unknown, and further studies have been recommended in the United States.[9]I n the U.K., recreational exposure to fresh water and swimming pools has been identified as a possible risk factor,[10,11,12] as well as travel to developing countries.[11] We set out to determine risk factors for giardiasis in residents of southwest England who had not recently traveled outside the U.K.