Symptoms and Testing
is an infection primarily of the small intestine caused by the
parasite Giardia lamblia. The parasite exists in cyst and
trophozoite forms; the infective stage is the cyst.1
While infection is often asymptomatic, it may be associated with
diarrhea, abdominal pain, flatulence, fatigue, anorexia, and
weight loss.2 The incubation period is 3 to 25 days
or longer (median 7 to 10 days).2 In patients with
diarrhea can lead to dehydration, malabsorption, and impairment
function.3. Diagnosis in acute cases is established
by the direct microscopic
examination of stool for the presence of cysts or trophozoites,
or detection of G. lamblia antigens in these specimens.3
In chronic cases, excretion is irregular, requiring repeated
stool examination. Alternatively, duodenal contents obtained
with a nylon string or by endoscopic aspiration can be
examined for trophozoites.4
Humans are the
principal reservoir, but Giardia can infect beavers,
cats, dogs, and other domestic and wild animals.1
This organism is the most common cause of intestinal parasitic
infection in humans world-wide.3 The infectious dose
is low: humans can be infected with as few as 10 cysts.5
Person-to-person transmission occurs by the fecal-oral route;
this is the principal mode of spread in institutions and day
care centers. Other modes of transmission include contaminated
food, drinking water, and recreational water.1 Cysts
can remain viable for 2-3 months in cold water and are resistant
to killing by routine chlorine treatments.3 They are,
however, destroyed by boiling water for 1 minute.1
Public water supplies that are exposed to human or animal feces
should be treated with a combination of filtration, chlorination
and stringent maintenance of distribution systems.5
Persons at greatest risk of exposure to infection are children
in day care, their close contacts, men who have sex with men,
backpackers and campers (via ingestion of unfiltered, untreated
drinking water), travelers to disease-endemic areas, and persons
drinking water from shallow wells.5 Most
community-wide outbreaks result from contaminated water
supplies.1 Hand washing after toilet use and before
handling food or eating is an important preventive measure,
especially in the day care setting.2 Adams and Perkin6
found that 29% of 65 children living in a rural northern Florida
tested positive for G. lamblia, and 56% of the youngest
(<5 years of age) children were found to be infected. Inadequate
water supplies were found for 70% of the families; all the
children were born in Florida and had not traveled outside the
Giardiasis in Florida
In 2000, 1520 cases of giardiasis were reported in Florida (9.7
cases per 100,000 population) with the highest incidence (47.6
per 100,000) in children 1-4 years of age.7 The last
five year average of confirmed cases was 908 per year, though
the incidence of suspected and probable cases is even higher.
Consistent with national data, cases occurred throughout the
year with peaks in July and August. The majority of cases
reported in the state appear to be related to person to person
transmission with outbreaks in day care settings not uncommon.
American Academy of Pediatrics. Georges P (ed.) 2000 Red
Book: Report of the Committee on
25th Edition. Elk Grove, IL, 1997; 210-212.
2. Benenson AS (ed.)
Control of Communicable Diseases Manual, 16th Edition.
United Book Press, Baltimore, MD,2000; 220-222.
3. Murray PR (ed.)
Manual of Clinical Microbiology, 7th Edition. ASM Press,
Washington, DC, 1999; 1399-1401.
4. Berkow R (ed.)
The Merck Manual of Diagnosis and Therapy, 16th Edition.
Merck Research Labs, Rathway, NJ, 1992; 228-229.
6. Adams RT and
Perkin JE. The prevalence of intestinal parasites in children
living in an
in rural northern Florida.
J School Health, 1985; 55 (2): 76-78.
7. Florida Department
of Health, Bureau of Epidemiology, Surveillance Section, 2000.