The Incidence of Campylobacter Infections
How common is Campylobacter infection?
From the time of its initial discovery, through the ensuing period of investigation and study, Campylobacter jejuni has come to be understood as one of the leading causes of bacterial gastroenteritis. [1, 5, 7]
In the United States, these bacteria are the most common cause of bacterial foodborne illness, ahead of Salmonella—the second most common cause. [1, 10, 25] According to the CDC, based on data collected through its Foodborne Disease Active Surveillance Network (or FoodNet):
Campylobacter is one of the most common causes of diarrheal illness in the United States. The vast majority of cases occur as isolated, sporadic events, not as part of recognized outbreaks. Active surveillance through FoodNet indicates that about 13 cases are diagnosed each year for each 100,000 persons in the population. Many more cases go undiagnosed or unreported, and campylo-bacteriosis is estimated to affect over 2.4 million persons every year, or 0.8% of the population. 
In 2006, 5,712 confirmed cases of Campylobacter infection were reported to the CDC through FoodNet.  Three years later, in 2009, there were 6,033 confirmed cases of Campylobacter infections, which represented an incidence rate of 13.02 cases for every 100,000 persons in the United States.  The 2009 numbers represented a reported 30% decrease in the number of infections compared to the 1996—1998 rates of infection. Although the nature and degree of underreporting is subject to dispute, all agree that the confirmed cases represent just the tip of the iceberg. Indeed, one study estimates the annual incidence rate for Campylobacter to be around 1,000 cases per 100,000 persons.  As early as 1990, it was noted that annual reports to the CDC of Campylobacter infections was as high as 10,000 lab-confirmed cases.