Results of FilmArray® Gastro-intestinal Panel and Serum Procalcitonin in Acute Colitis and Infectious Diarrhea in the ER

Acute diarrhea and acute colitis of infectious origin are common reasons for consultation at the emergency department. The current etiological diagnostic approach is limited to the determination of markers of inflammation, such as CRP and blood leukocytes, which lack specificity and sensitivity for bacterial infection. The stool culture can detect bacterial pathogens in the stool with a result at least 48 hours later and a positivity rate \<50%. This study will describe the procalcitonin (PCT) concentrations (a biomarker of bacterial infection) in this population to evaluate its usefulness depending on the viral or bacterial etiology identified by stool multiplex gastro-intestinal PCR panel (GI panel) and stool culture. The investigators hypothesize that PCT levels will be higher if the GI panel or the stool culture identifies a bacteria or a parasite, as it is the case in respiratory tract infections. If there is a detection of a virus by the GI panel or both the stool culture and the GI panel are negative, the investigators expect that PCT values will be lower or negative. the investigators will include the patients admitted to the ED with a suspicion of infectious diarrhea or acute colitis in order to have a large representative panel of infectious diarrhea etiologies. Only the patients having a blood sample prescribed as the routine care will be included. The blood sample is useful for dosing CRP and whole blood cell count (WBC), which are part of current biologic analyses performed in this context. After getting the patient's consent, the investigator will add the PCT dosage in blood sampling and will ask the patient to provide a stool sample, in order to have a stool culture and to perform an extended investigation for the pathogens through multiplex PCR technology (Filmarray ®GI panel). The physician will be asked if all these results (the ones ordered currently together with the dosage of PCT and the GI panel) will change his/her decision to start an an