How is Campylobacter infection diagnosed?
Campylobacter enteritis is often clinically indistinguishable from other viral or bacterial gastrointestinal illnesses. Diagnostic testing is not always indicated for children who present with acute diarrheal illnesses, with or without fever or vomiting, because determining the cause often does not change clinical management.
While stool culture is the gold standard for the identification of Campylobacter species, it can be difficult to isolate using standard culture media. Campylobacter grows best on media containing selective antibiotics and in microaerobic conditions with 5% to 10% oxygen, 1% to 10% carbon dioxide, and some hydrogen.
A diagnosis can also be established by the direct examination of a stool sample using contrast microscopy or Gram stain, during which the Campylobacter organism is identified by its characteristic appearance as a comma- or spiral-shaped gram-negative bacillus. This direct examination provides for a rapid presumptive diagnosis, but it can only be confirmed by stool culture.
Only a small percentage of persons suffering from Campylobacter infections both present for medical care and have their infections culture-confirmed. In the study of one Campylobacter outbreak, only 5.4% of the outbreak cases visited a physician.
Many persons submit samples for culturing after they have started antibiotics, which may make it even more difficult for a lab to grow Campylobacter. Blood cultures are often not performed and, in most cases, the bloodstream is not infected.
Newer technology picks up more infections, but has limitations.
The use of culture-independent diagnostic tests (CIDT) has been increasing in recent years. The 2016-2019 FoodNET data revealed a large increase in the number of infections diagnosed by CIDTs, whether the culture was positive or negative. Similarly, this data saw an increase in the number of infections that were diagnosed by stool culture alone.
CIDT tests are generally more sensitive and have faster turnaround times than traditional culture-based diagnostics. Reverse transcriptase polymerase chain reaction (PCR testing) identifies Campylobacter from stool 20% to 40% more frequently than culture-based methods. However, because these tests identify the presence of nucleic acid rather than viable organisms, the clinical significance is not always clear. The identification of multiple pathogens is not uncommon and can be difficult to interpret. In addition, CIDTs cannot be used to identify antibiotic susceptibility patterns. Unlike organisms such as Shigella and Salmonella, cultures of Campylobacter often are not performed automatically when the organism is detected by CIDT.
Antibiotic resistance to fluoroquinolones and tetracyclines is common in Campylobacter isolates, so if treatment is warranted and there is concern for resistance, cultures can still be beneficial after identification by CIDT.