- Conners EE, et al. MMWR Morb Mortal Wkly Rep. 2021;70:304-307, https://bit.ly/39ra67N.
Giardiasis is a diarrheal illness caused by the parasite Giardia intestinalis. Giardia is a flagellate protozoan that is transmitted by cysts spread via the fecal-oral route. Infection is limited to the small intestine and biliary tract and has a broad spectrum of clinical manifestations.
While approximately 50% of infections are asymptomatic, giardiasis can present with a range of gastrointestinal symptoms, including diarrhea, abdominal cramps, greasy stools, bloating, flatulence, nausea/vomiting, weight loss or dehydration. While illness often is self-limited in duration, it can be severe with a protracted, intermittent, often debilitating disease in which anorexia combined with malabsorption can lead to significant weight loss, failure to thrive and anemia.
Giardiasis consistently is the leading cause of intestinal parasitic infection in the United States. Humans are the principal reservoir of infection, with the highest incidence of cases among children 1-9 years of age. Outbreaks usually occur in child care centers or institutional care settings.
This report summarizes 2012-’17 surveillance data for Giardia outbreaks reported to the Centers for Disease Control and Prevention (CDC), including case counts, transmission mode, exposures and settings of infection.
Study results
The CDC, in conjunction with local, state and territorial health departments, manages enteric, foodborne and waterborne disease outbreak information via the National Outbreak Reporting System (NORS). The system maintains data on disease outbreaks caused by bacterial, viral, parasitic, chemical, toxin and unknown agents.
When reporting to NORS, clinicians can use the surveillance outbreak definition of giardiasis, which is the occurrence of two or more cases of illness epidemiologically linked to a common exposure. The case definition includes clinical and laboratory criteria.
During the study period, 111 giardiasis outbreaks with 760 primary cases were reported across 26 states. There were 28 hospitalizations, 48 emergency department visits and no deaths. Pennsylvania (40%) and Minnesota (10%) reported the largest number of outbreaks (see map). Outbreaks did not differ significantly by year.
The most common mode of transmission across all years was waterborne exposure (370 cases), including tap water systems (nine outbreaks), outdoor freshwater consumption (seven outbreaks) and recreational water (nine outbreaks). Person-to-person transmission occurred in 129 cases, mostly in private residences (50%) and child care facilities (43%). Of the cases in private homes, the majority occurred in households with children 5 years of age and younger.
Implications for pediatrics
Giardiasis continues to be the most common intestinal parasitic infection in the United States. Most communitywide outbreaks from 2012-’17 resulted from contaminated water exposure.
While some infections are self-limited, severe infection can occur, leading to dehydration and electrolyte abnormalities requiring emergency department visits and hospitalization.
Given that NORS is a passive surveillance system that depends on community reporting, it is essential for clinicians to have a high suspicion for Giardia infection.
Maintaining surveillance not only will improve clinical recognition of these parasitic infections but also will provide better understanding of their epidemiology, seasonality and geographic distribution. Knowledge of the epidemiology of giardiasis helps identify outbreaks more rapidly and improves prevention efforts.
Health care providers, especially pediatricians, are critical to promoting community prevention efforts, including endorsing good hand hygiene practices. Patients with giardiasis might be infectious for several weeks, and ingestion of as few as 10 cysts can cause disease.
In addition, health care providers should encourage prompt diagnosis and treatment, cleaning and disinfecting home environments and child care facilities, and monitoring water quality in private wells.
In addition to the more common causes of acute gastroenteritis encountered in clinical practice, the differential diagnosis should include Giardia, which will enhance the identification and reporting of cases.
Dr. Goldstein is a post-graduate training fellow in pediatric infectious diseases at Emory University School of Medicine. Dr. Pickering is adjunct professor of pediatrics at Emory University School of Medicine.
