A comparison of cytomegalovirus and community respiratory viruses in immunocompromised patients

High-resolution computed tomography (HRCT) of lung infections in non-AIDS immunocompromised patients

Non-AIDS immunocompromised patients are susceptible to infections by a wide range of organisms. In the past several decades, advances in the treatment of cancer, organ transplantation, and immunosuppressive therapy have resulted in large numbers of patients who develop abnormalities in their immune system. Moreover, mildly impaired host immunity as it occurs in chronic debilitating illness, diabetes mellitus, malnutrition, alcoholism, advanced age, prolonged corticosteroid administration, and chronic obstructive lung disease have also been regarded as predisposing factors of pulmonary infections. Imaging plays a crucial role in the detection and management of patients with pulmonary infectious diseases. When pulmonary infection is suspected, knowledge of the varied radiographic manifestations will narrow the differential diagnosis, helping to direct additional diagnostic measures and serving as an ideal tool for follow-up examinations. Combination of pattern recognition with knowledge of the clinical setting is the best approach to pulmonary infection occurring in the immunocompromised patients.

Viral prophylaxis in organ transplant patients

Viral pathogens have emerged as the most important microbial agents having deleterious effects on solid organ transplant (SOT) recipients. Antiviral chemoprophylaxis involves the administration of medications to abort transmission of, avoid reactivation of, or prevent progression to disease from, active viral infection. Cytomegalovirus (CMV) is the major microbial pathogen having a negative effect on SOT recipients. CMV causes infectious disease syndromes, augments iatrogenic immunosuppression and is commonly associated with opportunistic superinfection. CMV has also been implicated in the pathogenesis of rejection. Chemoprophylactic regimens for CMV have included oral aciclovir (acyclovir) at medium and high doses, intravenous and oral ganciclovir, and the prodrugs valaciclovir (valacyclovir) and valganciclovir. CMV prophylactic strategies should be stratified, with the highest-risk patients receiving the most 'potent' prophylactic regimens. Herpes simplex virus (HSV) reactivation in SOT recipients is more frequent, may become more invasive, takes longer to heal, and has greater potential for dissemination to visceral organs than it does in the immunocompetent host. Prophylactic regimens for CMV are also effective chemoprophylaxis against HSV; in the absence of CMV prophylaxis, aciclovir, valaciclovir or famciclovir should be used as HSV prophylaxis in seropositive recipients. Primary varicella-zoster virus (VZV) after SOT is rare and most commonly seen in the paediatric transplant population because of VZV epidemiology. Zoster occurs in 5-15% of patients, usually after the sixth post-transplant month. Prophylactic regimens for zoster are neither practical nor cost effective after SOT because of the late onset of disease and low proportion of affected individuals. All SOT recipients should receive VZV immune globulin after contact with either varicella or zoster. Epstein-Barr virus has its most significant effect in SOT as the precipitating factor in the development of post-transplant lymphoproliferative disorders. Antiviral agents that could be effective are the same as those used for CMV, but indications for and effectiveness of prophylaxis are poorly established. Hepatitis B virus (HBV) and hepatitis C virus (HCV) are important pathogens in the SOT population as indications for transplantation. So-called 'prophylaxis' for recurrent HBV and HCV after liver transplantation is controversial, suppressive rather than preventive, and potentially lifelong. Influenza infection after SOT is acquired by person-to-person contact. During epidemic periods of influenza, transplant populations experience a relatively high frequency of infection, and influenza may affect immunosuppressed SOT recipients more adversely than immunocompetent individuals. Antiviral medications for prevention of influenza are administered as post-exposure prophylaxis to SOT recipients, in addition to yearly vaccine, in circumstances such as influenza epidemics and nosocomial outbreaks, and after exposure to a symptomatic individual during 'flu season'.

Pulmonary Infiltrates in the Non-HIV-Infected Immunocompromised Patient

Pulmonary complications remain a major cause of both morbidity and mortality in immunocompromised patients. When such individuals present with radiographic infiltrates, the clinician faces a diagnostic challenge. The differential diagnosis in this setting is broad and includes both infectious and noninfectious processes. Rarely are the radiographic findings classic for one disease, and most potential etiologies have overlapping clinical and radiographic appearances. In recent years, several themes have emerged in the literature on this topic. First, an aggressive approach to identifying a specific etiology is necessary; as a corollary, diagnostic delay increases the risk for mortality. Second, the evaluation of these infiltrates nearly always entails bronchoscopy. Bronchoscopy allows identification of some etiologies with certainty, and often allows for the exclusion of infectious agents even if the procedure is otherwise unrevealing. Third, early use of CT scanning regularly demonstrates lesions missed by plain radiography. Despite these advances, initial therapeutic interventions include the use of broad-spectrum antibiotics and other anti-infectives in order to ensure that the patients is receiving appropriate therapy. With the results of invasive testing, these treatments are then narrowed. Frustratingly, outcomes for immunocompromised patients with infiltrates remain poor.

A randomized, double-blind trial comparing azithromycin and clarithromycin in the treatment of disseminated Mycobacterium avium infection in patients with human immunodeficiency virus

Two hundred and forty-six patients infected with human immunodeficiency virus (HIV) who also had disseminated Mycobacterium avium complex received either azithromycin 250 mg every day, azithromycin 600 mg every day, or clarithromycin 500 mg twice a day, each combined with ethambutol, for 24 weeks. Samples drawn from patients were cultured and clinically assessed every 3 weeks up to week 12, then monthly thereafter through week 24 of double-blind therapy and every 3 months while on open-label therapy through the conclusion of the trial. The azithromycin 250 mg arm of the study was dropped after an interim analysis showed a lower rate of clearance of bacteremia. At 24 weeks of therapy, the likelihood of patients' developing 2 consecutive negative cultures (46% vs. 56%, P=.24) or 1 negative culture (59% vs. 61%, P=.80) was similar for azithromycin 600 mg (n=68) and clarithromycin (n=57), respectively. The likelihood of relapse was 39% versus 27% (P=.21) on azithromycin compared with clarithromycin, respectively. Of the 6 patients who experienced relapse, none of those randomized to receive azithromycin developed isolates resistant to macrolides, compared with 2 of 3 patients randomized to receive clarithromycin [corrected]. Mortality was similar in patients comprising each arm of the study (69% vs. 63%; hazard, 95.1% confidence interval, 1.1 [0.7, 1.7]). Azithromycin 600 mg, when given in combination with ethambutol, is an effective agent for the treatment of disseminated M. avium disease in patients infected with HIV.