4 Adult Gastrointestinal Infections

FIGURE 88.4.2 Flow chart showing approach to the evaluation of a patient with acute infectious diarrhea.

Once disease onset, presentation, and progression of associated symptoms are evaluated, and immediate laboratory work has been performed, it may be useful to categorize the diarrhea into one of two physiologic classifications: noninflammatory and inflammatory (Table 88.4.24). A subcategory of inflammatory is hemorrhagic or dysenteric diarrhea; distinction of the specific type of diarrhea is helpful to focus on appropriate empiric management options.

TABLE 88.4.24 Classification of Acute Diarrhea Based on Findings of Fecal Markers of Inflammation (Leukocytes or Lactoferrin) or Presence of Gross Fecal Blood

FIGURE 88.4.3 Relative importance of etiologic agents in hospital-acquired diarrhea. This figure shows the percentage of incidence of each of the common diarrhea-causing bacteria. CDI, *Clostridium difficile* infection; IBD, inflammatory bowel disease. (Adapted from McFarland LV. Epidemiology of infectious and iatrogenic nosocomial diarrhea in a cohort of general medicine patients. *Am J Infect Control.* 1995;23(5):295–305.)

Health Care–acquired Diarrhea

Illness occurring after the 72 hours in the hospital or nursing home can be considered health care–associated. In Fig. 88.4.3, the relative importance of causes of diarrhea in hospitalized patients in one study is provided. Between 10% and 30% of nosocomial diarrhea is due to C. difficile; since 10% to 20% of institutionalized patients are colonized with this organism during hospitalization and because most acute diarrhea developing in the hospital is not caused by C. difficile the PCR test for fecal toxin often gives a false-positive result (6).

The other important causes of nosocomial diarrhea include antibiotics, chemotherapeutic agents, PPIs, tube feedings, laxatives, other drugs, and various iatrogenic and idiopathic conditions (see Fig. 88.4.3).

It is appropriate, in all hospital-associated diarrheas when a patient is receiving antibacterial treatment, to consider C. difficile as the causative agent, and empiric treatment is advisable only in the more severe cases while laboratory tests are pending. Rarely, other pathogens can be found in hospital- and nursing home–associated diarrhea, including rotaviruses.

The International Traveler Returning with Diarrhea

TD may occur when persons travel from industrialized to developing tropical and semitropical areas with reduced levels of personal and food hygiene. TD is the most common travel-related infectious illness, occurring in up to 40% of travelers to regions of Asia, Africa, and Latin America. Among US travelers, the majority of cases of TD occur in individuals returning from Latin America and the Caribbean, but the greatest risk is noted after travel to the Indian subcontinent (7); bacterial enteropathogens cause as much as 80% of TD cases.

The world has been classified into three different risk groups: low, intermediate, and high risk, based on the frequency of TD in the traveling public. The important causes of TD are Enterotoxigenic E. coli (ETEC), enteroaggregative E. coli (EAEC), noroviruses, Campylobacter, Shigella, and Salmonella. Less commonly, parasitic agents cause TD and should be suspected in persistent illness; important parasitic pathogens include Giardia, Cryptosporidium, and Cyclospora. Patients with TD should be treated empirically with antibiotics without stool examination.

Immunosuppressed Patient with Diarrhea

An immunosuppressed or immunocompromised patient, including those with congenital or acquired immune deficiency, HIV/AIDS, receipt of immunosuppressive, or cancer chemotherapy drugs, will have increased susceptibility to diarrhea. The etiology of diarrheal diseases in immunocompromised hosts is different from that of other populations in that they are at risk of developing infections from various opportunistic organisms in addition to the routine diarrheal pathogens. The use of various chemotherapy drugs or immunomodulators, such as cyclosporine, mycophenolate mofetil, tacrolimus, or sirolimus may result in drug-induced diarrhea (8); diarrhea in transplant recipients can also be due to graft versus host disease (GVHD). The most commonly identified organisms to consider as causes of diarrhea in this group of patients are C. difficile and noroviruses; other causes are Salmonella, Cryptosporidium, Isospora, Cyclospora, cytomegalovirus, and Mycobacterium avium–intracellulare complex. A thorough and quick evaluation for identifying the causative organism is the key in treating and controlling diarrhea in this patient population. Appropriate rapid diagnostic tests may include direct stool examination for ova, cysts, and parasites; stool test for C. difficile toxin; polymerase chain reaction (PCR) for cytomegalovirus or herpesvirus; stool cultures; and blood cultures. If the above tests do not provide a specific diagnosis, endoscopy and mucosal biopsy should be pursued to establish an etiologic diagnosis (9). Abdominal computed tomography (CT) may detect mucosal thickening or other changes of ischemic, hemorrhagic, or inflammatory colitis, and it is the preferred diagnostic study when both intra-abdominal disease and intestinal disease are expected (10).

Patient with Extraintestinal Disease and Diarrhea

Diagnostic evaluation of patients with diarrhea and systemic symptoms and signs will often take the clinician’s focus away from the gut for the diagnosis. Blood cultures, CT of the abdomen, and serology (for Entamoeba histolytica) may help determine the primary cause of the disease. In cases of sepsis, blood cultures and stool studies may provide the diagnosis; systemic complications are often seen with invasive bacterial and parasitic infections. Systemic complications of enteric infection include hemolytic uremic syndrome (HUS) or thrombotic thrombocytopenic purpura (TTP), Guillain–Barré syndrome, reactive arthritis, iritis, postinfectious irritable bowel syndrome, sepsis, infective endocarditis, and abdominal abscesses or localized abscess elsewhere, or pyogenic arthritis. In immunocompromised patients with diarrhea, systemic complications can occur with any of the etiologic agents. Antimotility drugs should not be used in dysenteric and febrile diarrhea without effective concomitant antibiotics as they can prolong or complicate the disease. Amoebiasis, which is uncommon in the United States, shows an extended spectrum of extraintestinal complications including liver abscess and disseminated infection.

TABLE 88.4.25 Classification of Dehydration in a Patient with Acute Diarrhea (11)

MANAGEMENT OF ACUTE DIARRHEA

Dehydration

Dehydration is defined as excess loss of body fluids resulting in fluid and electrolyte abnormalities; classifications of dehydration are provided (Table 88.4.25).

Dry skin and dry mucous membranes, sunken eyes, decreased urine output, loss of skin turgor, dizziness/light-headedness are all manifestations of moderate to severe dehydration. Dehydration is the most common serious complication of diarrhea and should be promptly recognized and managed in all patients. Patients in an ICU, with other comorbid conditions and extremes of age, need to be vigorously treated to avoid life-threatening complications of dehydration. Routine testing of electrolytes in patients with severe diarrhea offers some value in guiding fluid management in the ICU setting (12).

Rehydration can be done depending on severity of the dehydration either by oral or i.v. routes. Where available, oral rehydration salt (ORS) solution can be used in mild or moderate dehydration and for maintenance of hydration after i.v. fluid administration in severe dehydration. Standard or reduced osmolarity (low salt) ORS formulations are preferable where available. In dehydration due to cholera-like profuse watery diarrhea with massive fluid loses, reduced-osmolarity ORS may lead to subclinical reduction of body electrolytes, making standard ORS preferable in this dehydrating form of diarrhea for outpatients (13). In the United States, ORS is not readily available, but Pedialyte or Ricelyte can be used to maintain hydration and treat minor degrees of dehydration for outpatients. For inpatients with cholera-like diarrhea in the United States, i.v. fluids are preferentially used; specific fluid replacement strategies based on severity are presented in Table 88.4.25.

Dysentery

Dysentery is defined as passage of bloody stools suggesting bacterial colitis (14). The four major causes of bloody diarrhea in the United States, in descending order of frequency of occurrence, are Shigella, Campylobacter, nontyphoid Salmonella, and Shiga toxin–producing E. coli (15). Single cases of dysentery with high fever should be treated with azithromycin empirically. For nonfebrile or low-grade fever with dysentery in an outbreak with multiple cases, stools studies should be performed to look for the etiology, including Shiga toxin–producing E. coli, before considering therapy. Empiric and specific antibiotic treatments are provided in Tables 88.4.26 and 88.4.27.