Doctors often suspect C. difficile in anyone who has diarrhea and who has other risk factors for C. difficile. 

Clostridium difficile (klos-TRID-e-um dif-uh-SEEL), also known as Clostridioides difficile and often referred to as C. difficile or C. diff, is a bacterium that can cause symptoms ranging from diarrhea to life-threatening inflammation of the colon.

Illness from C. difficile most commonly affects older adults in hospitals or in long-term care facilities and typically occurs after use of antibiotic medications. However, studies show increasing rates of C. difficile infection among people traditionally not considered to be at high risk, such as young and healthy individuals who haven't used antibiotics and who haven't been in a health care facility.

Each year in the United States, about a half million people get sick from C. difficile, and in recent years, C. difficile infections have become more frequent, severe and difficult to treat. Recurrent C. difficile infections also are on the rise.

C difficile can produce two toxins, designated A and B, that have pathogenic effects in humans. Antibiotic-associated pseudomembranous colitis has been shown to result from the action of these two toxins. This disease has been associated with clindamycin use but it is now recognized that pseudomembranous colitis can follow administration of virtually any antibiotic. More than 70 percent of the cases in a large series were associated with cephalosporin therapy. The clinical spectrum of antibiotic-induced syndromes caused by C difficile includes patients with symptoms of acute abdomen with little or no diarrhea, as well as cases with fulminant life-threatening diarrhea. Nosocomial transmission and reinfection with different strains occurs as do spontaneous cases without prior antimicrobial therapy. In cases where cessation of antibiotic therapy does not produce a response, specific therapy with oral vancomycin, metronidazole, or oral bacitracin may be effective. Detection of the toxins produced by C difficile (rather than culture of the organism) is important in the determining therapy of this potentially fatal disease.

EIA:

EIA stands for Enzyme immunoassay. The enzyme immunoassay (EIA) test is faster than other tests but isn't sensitive enough to detect many infections and has a higher rate of falsely normal results. For more than 20 years the detection of toxin A/B from fecal samples by immunoenzymatic methods has been the cornerstone of laboratory CDI diagnosis. Toxin enzyme immunoassays (EIAs) are more rapid and easier to perform than culture or cytotoxin assays, they do not require special equipments or a dedicated technician, and the turnaround time allows the laboratory to refer results within the same day of specimen arrival. However, the performance of immunoenzymatic kits for C. difficile toxin(s) detection available on the market versus gold-standard methods is currently considered suboptimal (both in terms of sensitivity and specificity) if used as standalone assays. 

References:

https://jcm.asm.org/content/51/3/869