Opportunistic infections due to protozoan or fungal agents do not occur in patients with colorectal carcinoma. Nevertheless these subjects may become infected with members of the normal bacterial flora of the gut which are provided with a site for penetration of the colonic mucosal barrier by the invasive or necrotizing tumor. Bacteroides sepsis, Clostridium septicum and other clostridial infections (in the absence of deep traumatic lesions), and left perinephric abscess caused by coliforms and fecal streptococci appear to be characteristic associations with colonic neoplasia. In the absence of a known colonic lesion, diagnostic workup should be performed in all such patients. Barium enema would similarly be indicated in older patients with bacterial endocarditis in whom the portal of entry of the organism was not known. Am. I. Clin. Nut,'. 27: 1481-1485, 1974. Carcinoma of the colon and rectum is a common malignancy of older patients with a peak incidence in the 7th decade of life. It accounts for about 1 5% of all deaths due to cancer, and is surpassed in this morbid statistic only by carcinoma of the lung. About 2.5% of all deaths in the United States are attributable to colorectal carcinoma alone. A significant proportion of these fatalities is related to infection (1) of which over 90% can be traced in turn to necrotic or ulcerated tumors, obstruction of the gut or urinary tract by large, compressing tumor masses, chemotherapy or radiation-induced mucosal lesions, perforation or peritonitis. Neutropenia is rarely a problem, in contrast to the situation prevailing in patients with leukemias or lymphomas. Over the past two decades, the concepts of the compromised host and the opportunistic pathogen have received prominence as increas- ing numbers of patients with ultimately fatal diseases survive for longer periods of time due to improved therapeutic modalities or life- support systems. These patients may thus live another day, but each day begins with the potential for a fatal encounter with ubiquitous microorganisms in the environment or members of the indigenous microbiota. Man normally lives in a state of delicate balance with a variety of microorganisms capable of provoking life- threatening illness if they can reach the right site in the body in sufficient numbers to overcome the multiplicity of defense mecha- nisms possessed by the host. Thus the host receiving immunosuppressive or cytotoxic chemotherapy, antibiotics which alter the qual- ity and/or quantity of this flora, in whom invasive disease processes or procedures breech intact surface barriers to penetration by micro- organisms, is compromised in his ability to resist infection. These significant alterations in the host predispose him to invasion by agents which normally live in close association with man as saprophytic commensal organisms. Because these generally noninvasive agents take advantage of the opportunity offered by a compromised host they have been called oppor- tunistic pathogens, and the diseases they cause,
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