Incidence of acute gastroenteritis and role of norovirus, Georgia, USA, 2004-2005

Abstract

Approximately 179 million cases of acute gastroenteritis (AGE) occur annually in the United States. However, lack of routine clinical testing for viruses limits understanding of their role among persons seeking medical care. Fecal specimens submitted for routine bacterial culture through a health maintenance organization in Georgia, USA, were tested with molecular diagnostic assays for norovirus, rotavirus, astrovirus, sapovirus, and adenovirus. Incidence was estimated by using national health care utilization rates. Routine clinical diagnostics identified a pathogen in 42 (7.3%) of 572 specimens; inclusion of molecular viral testing increased pathogen detection to 15.7%. Community AGE incidence was 41,000 cases/100,000 person-years and outpatient incidence was 5,400/100,000 person-years. Norovirus was the most common pathogen, accounting for 6,500 (16%) and 640 (12%) per 100,000 person-years of community and outpatient AGE episodes, respectively. This study demonstrates that noroviruses are leading causes of AGE among persons seeking medical care.

Figure 1

Equations used for calculation of community and outpatient incidence of each pathogen in patients with acute gastroenteritis (AGE), Kaiser Foundation Health Plan of Georgia, Inc., USA, March 15, 2004–March 13, 2005. P_i, prevalence of pathogen i in stool samples; S, total no. stool samples submitted; ComSS_i, pathogen-specific fecal specimen submission rates among all respondents with AGE; N, total Kaiser membership; OutSS_i, pathogen-specific fecal specimen submission rates among those seeking medical care; S_ia, no. of stools positive for pathogen i in age group a; ComSS_a, proportion of those in age group a with AGE who seek care and submit stool specimen; OutSS_a, proportion of those in age group a seeking care for AGE who submit stool specimen.

Figure 2

Pathogen prevalence in acute gastroenteritis outpatients by season, Kaiser Foundation Health Plan of Georgia, Inc., USA, March 15, 2004–March 13, 2005. Viral pathogens predominated during winter and spring, and bacteria predominated during summer and fall.

Figure 3

Distribution of norovirus genotypes among 25 outpatients with acute gastroenteritis, Kaiser Foundation Health Plan of Georgia, Inc., USA, March 15, 2004–March 13, 2005. Genogroup II (GII) was more prevalent than GI. *Includes GII.2 (2 specimens), GII.14 (2 specimens), and GII.17 (1 specimen).