A group of researchers is investigating the causative agents responsible for infections in immunocompromised individuals. Patients with solid-organ malignancy who have received conventional chemotherapy are enrolled in the study. Detailed microbiologic data are obtained on any patient who develops fever during chemotherapy-induced neutropenia. Which of the following types of pathogens are most likely to be obtained in the majority of these patients?

Question

A group of researchers is investigating the causative agents responsible for infections in immunocompromised individuals.  Patients with solid-organ malignancy who have received conventional chemotherapy are enrolled in the study.  Detailed microbiologic data are obtained on any patient who develops fever during chemotherapy-induced neutropenia.  Which of the following types of pathogens are most likely to be obtained in the majority of these patients?

Quizplus · Accepted Answer

Systemic chemotherapy targets rapidly dividing cancer cells but often incidentally damages other rapidly dividing cells in the gastrointestinal tract and bone marrow, which dramatically increases the risk of infection due to: Mucositis - Damage to rapidly dividing epithelial cells of the digestive tract creates breaches in the mucosal barrier that allow endogenous bacterial flora (commensal organisms) to penetrate and enter the bloodstream. Gram-negative enteric bacilli, such as Pseudomonas aeruginosa, and gram-positive skin organisms, such as Staphylococcus epidermidis and S aureus, are most likely to invade. Neutropenia - Damage to rapidly dividing granulopoietic cells reduces circulating neutrophil count. Because neutrophils serve as front-line defense against bacterial and fungal pathogens, commensal pathogens that penetrate the mucosal/cutaneous barrier cannot be contained and subsequently spread to the bloodstream and deeper tissues. Neutropenic patients have weak inflammatory responses and fever is often the only sign of infection (neutropenic fever). To reduce the risk of serious infection, patients who receive systemic chemotherapy are often empirically treated with prophylactic antibiotics (eg, ciprofloxacin) to prevent commensal organisms from invading and with granulocyte-stimulating agents (eg, filgrastim) to increase neutrophil count. (Choice A) Environmental pathogens such as Histoplasma (in bird droppings), Mycobacterium avium complex (in water), and Cryptococcus (in soil contaminated by bird droppings) often cause opportunistic infection in those with advanced AIDS due to impaired cell-mediated immunity. Although these pathogens can cause infections in those with neutropenia, most cases of neutropenic fever are due to endogenous commensal organisms. (Choice B) Hospital-acquired, drug-resistant bacteria, such as methicillin-resistant S aureus, can cause neutropenic fever but do so much less often than endogenous commensal bacteria. (Choice C) Pathogens spread from infected contacts (eg, influenza) are more likely to cause severe infection in those with impaired immunity. However, the greatest cause of neutropenic fever is endogenous bacterial flora. (Choice E) The reactivation of latent bacterial (eg, tuberculosis) and viral (eg, cytomegalovirus) pathogens is common in those with impaired cellular immunity (eg, AIDS, immunosuppression). However, endogenous commensal bacteria are a more likely cause of fever in neutropenic patients. Educational objective: Chemotherapy-associated neutropenic fever is most often caused by endogenous commensal bacteria that have translocated across damaged mucosal sites. __________ References: Microbial etiology of febrile neutropenia. (http://www.ncbi.nlm.nih.gov/pubmed/21629636)

A Group of Researchers Is Investigating the Causative Agents Responsible