CT of viral lower respiratory tract infections in adults: comparison among viral organisms and between viral and bacterial infections.

OBJECTIVE: We retrospectively compared the CT findings of consecutive viral and bacterial lower respiratory tract infections (LRTIs) to determine their imaging appearance and any definable differences among the causative viruses and between the viral and bacterial infections. MATERIALS AND METHODS: Imaging features of LRTI caused by influenza virus, respiratory syncytial virus (RSV), parainfluenza, adenovirus, and bacteria over a 33-month period were reviewed by three radiologists blinded to clinical and diagnostic information. Individual CT features and the dominant pattern of infection were recorded for each examination. Imaging characteristics were compared among the four respiratory viruses and between viral and bacterial infections. RESULTS: One hundred fifteen chest CT scans were analyzed (60 influenza virus, 19 RSV, 10 adenovirus, four parainfluenza virus, and 22 bacterial pneumonia LRTIs). Individual imaging findings and imaging patterns were seen in similar frequencies when we compared viral and bacterial LRTIs, with the exception of the diffuse airspace pattern, which was seen more frequently in bacterial infections. Although there was overlap in the imaging appearance of individual viruses, RSV and adenovirus tended to have characteristic imaging appearances. RSV presented with an airway-centric pattern of disease (13/19 cases [68%]) characterized by varying mixtures of tree-in-bud opacities and bronchial wall thickening, with or without peribronchiolar consolidation. Adenovirus typically appeared as multifocal consolidation or ground-glass opacity without airway inflammatory findings (7/10 cases [70%]). CONCLUSION: There is considerable overlap in the imaging appearance of viral and bacterial respiratory infections. However, some characteristic differences can be seen, especially with RSV and adenovirus infections.

Chest computed tomographic imaging characteristics of viral acute lower respiratory tract illnesses: a case-control study.

OBJECTIVE: This study aimed to determine whether computed tomographic (CT) findings can distinguish viral lower respiratory tract illness (LRTI) from other conditions. METHODS: Three radiologists reviewed CT images of patients with LRTI who underwent testing for respiratory viral infection. Imaging findings in subjects with positive viral assays were compared with subjects with negative assays. RESULTS: Of 334 subjects, 93 were positive for viral LRTI. Tree-in-bud opacities and bronchial wall thickening were observed more often in subjects with viral LRTI (P < 0.05). Multifocal airspace disease occurred with similar frequency in both groups. Diffuse airspace opacification was negatively associated with viral LRTI. Pleural effusion was observed more often among subjects without viral LRTI (P < 0.001). CONCLUSIONS: Airway inflammatory changes such as tree-in-bud opacities, bronchial wall thickening, and peribronchiolar consolidation are associated with community-acquired viral LRTI. Recognition of these findings should prompt testing for viral infection. Multifocal consolidation is commonly found in cases of viral LRTI but is nonspecific.

The use of antimicrobial agents after diagnosis of viral respiratory tract infections in hospitalized adults: antibiotics or anxiolytics?

OBJECTIVE: Because extensive antibiotic use by inpatients has been associated with the development of multidrug-resistant organisms, we aimed to determine which variables were associated with the use of antibiotics after viral respiratory tract infection diagnosis among adult patients admitted to the hospital with respiratory symptoms. METHODS: A retrospective cohort study was conducted at 2 affiliated urban hospitals in Pennsylvania. We identified all adult patients admitted to the hospital during the period from November 1, 2005, through August 1, 2007, with a viral assay positive for influenza A or B, parainfluenza, adenovirus, or respiratory syncytial virus. Among these patients, we identified those who received antibiotics after the diagnosis of viral RTI. Data on demographics; comorbidities; and physical examination, laboratory, and radiographic findings were ascertained to identify risk factors for antimicrobial use among these patients. RESULTS: A total of 196 hospitalized patients with positive viral assay results were included; 125 of 131 patients administered antibiotics continued to receive them after viral RTI diagnosis. Among 52 patients with an abnormal chest radiograph, 46 continued antibiotic therapy. An abnormal chest radiograph was independently associated with continued antibiotic use (adjusted odds ratio, 4.28 [95% confidence interval, 1.71-10.77]; P = .002). However, the majority of patients (79 of 125 [63%]) who continued antibiotic therapy had normal chest imaging findings. Eight patients (6%) who continued antibiotic therapy and no patients who stopped developed C. difficile infection (95% CI, 1.5-∞; P = .05), but there was no significant difference in length of stay or mortality. CONCLUSIONS: Antibiotics are commonly used to treat hospitalized patients with known acute viral RTIs. Continued use is strongly associated with abnormal radiograph findings at admission. However, the reasons for continuation of antibiotics in the treatment of the majority of patients with normal radiographs are unclear and may represent inappropriate use.

Differences in the epidemiological characteristics and clinical outcomes of pandemic (H1N1) 2009 influenza, compared with seasonal influenza.

BACKGROUND: There are limited data comparing the clinical presentations, comorbidities, and outcomes of patients with infections due to seasonal influenza with patients with infections due to pandemic (H1N1) 2009 influenza. OBJECTIVE: To compare the epidemiological characteristics and outcomes of pandemic (H1N1) 2009 influenza with those of seasonal influenza. METHODS: A cross-sectional study was conducted among patients who received diagnoses during emergency department and inpatient encounters at 2 affiliated academic medical centers in Philadelphia, Pennsylvania. Cases of seasonal influenza during the period November 1, 2005, through June 1, 2008, and cases of pandemic influenza during the period from May 1, 2009, through August 7, 2009, were identified retrospectively. RESULTS: Forty-nine cases of pandemic influenza and 503 cases of seasonal influenza were identified. Patients with pandemic H1N1 were younger (median age, 29 years) than patients with seasonal influenza (median age, 59 years) (P<.001). More patients with pandemic H1N1 (35 [71%] of 49) were African American, compared with patients with seasonal influenza (267 [53%] of 503; P=.02). Several symptoms were more common among patients with pandemic influenza infections than among patients with seasonal influenza infections: cough (98% vs 83%; P=.007), myalgias (71% vs 46%; P=.001), and pleuritic chest pain (45% vs 15%; P<.001). Pregnancy was the only comorbidity that occurred significantly more often in the pandemic influenza group than in the seasonal influenza group (16% vs 1%; P<.001). There were no significant differences in frequencies of deaths of hospitalized patients, intensive care unit admission, or length of hospitalization between groups. CONCLUSION: Other than pregnancy, there were few clinically important differences between infections due to seasonal influenza and those due to pandemic influenza. The greater rate of lower respiratory tract symptoms in pandemic cases might serve to differentiate pandemic influenza from seasonal influenza.

Chest CT features of community-acquired respiratory viral infections in adult inpatients with lower respiratory tract infections.

PURPOSE: The appearance of respiratory virus infection on thoracic computed tomography (CT) has been described only to a limited extent in the current literature, and viral pneumonias may be under-recognized by radiologists. Our objective was to describe thoracic CT findings in a broad range of adult inpatients with respiratory virus infections. MATERIALS AND METHODS: A retrospective analysis of chest CTs was performed on symptomatic adult inpatients presenting with positive nucleic acid-based assays for 1 of 4 common community-acquired respiratory viruses. Forty-two patients with viral respiratory tract infections who underwent chest CT imaging were evaluated. The reviewer was blinded to virus type and patient information. CT findings were compared with CT reports produced at the time of the original study and correlated with clinical outcome measures. RESULTS: Influenza (n=21), adenovirus (n=9), respiratory syncytial virus (n=8), and parainfluenza (n=4) were represented among the cohort. Three patterns of the disease were seen with viral infection: (1) limited infection with normal imaging (21%), (2) bronchitis/bronchiolitis characterized by bronchial wall thickening and tree-in bud opacities (31%), and (3) pneumonia characterized by multifocal consolidation or ground-glass opacities (36%). Viral infection was suggested in only 4/42 (10%) of the original radiology reports, all of which had evidence of bronchitis/bronchiolitis on chest CT. Viral pneumonia, characterized by multifocal ground-glass opacities or multifocal consolidations, was interpreted as aspiration pneumonia or bacterial pneumonia in 15/16 (94%) of the original CT reports. CONCLUSIONS: CT scans of the inpatients with community-acquired viral infections most commonly show 1 of 2 patterns: consolidation and ground-glass opacities or bronchial wall thickening and tree-in-bud opacities. It is important that physicians interpreting CTs with multifocal consolidations and/or multifocal ground-glass opacities consider viral pneumonia when these findings are observed and recommend appropriate diagnostic testing when clinically warranted.

Treating viral respiratory tract infections with antibiotics in hospitals: no longer a case of mistaken identity.

Widespread use of antibiotics in hospitalized patients contributes to the development of multidrug resistant organisms that make many infections increasingly difficult to treat. Despite calls to prescribe antibiotics judiciously, many physicians continue to order antibiotics for inpatients who do not need them. This Issue Brief investigates antibiotic use in hospitalized adults with a confirmed viral infection, a group of patients that may not benefit from such therapy. Understanding the factors that lead to inappropriate antibiotic use may help change clinical practice and limit antibiotic resistance.

Increased incidence of cytomegalovirus infection in high-risk liver transplant recipients receiving valganciclovir prophylaxis versus ganciclovir prophylaxis.

Optimal measures for the prevention of cytomegalovirus (CMV) in high-risk orthotopic liver transplant (OLT) patients are unknown. The charts of high-risk OLT recipients with 12 months of follow-up who were transplanted over a 44-month period were reviewed. The incidence of CMV disease in CMV-seropositive donor/CMV-seronegative recipient patients receiving valganciclovir or ganciclovir prophylaxis was compared. Sixty-six patients met the inclusion criteria and were treated with 1 of 3 prophylactic regimens: valganciclovir (900 mg daily; 27 patients), oral ganciclovir (1000 mg every 8 hours; 17 patients), or intravenous ganciclovir (6 mg/kg daily; 22 patients). Eight CMV cases occurred, all after completion of the prophylaxis. The combined incidence of CMV disease with intravenous and oral ganciclovir was lower than the incidence in valganciclovir recipients (P = 0.056; relative risk, 4.33; 95% confidence interval, 0.94-19.87). CMV disease occurred in 22.2% of valganciclovir recipients, 4.5% of intravenous ganciclovir recipients, and 5.9% of oral ganciclovir recipients. In conclusion, late-onset CMV disease occurred more frequently among high-risk liver transplant recipients treated with valganciclovir prophylaxis. The 4-fold higher incidence of CMV disease in our study supports the avoidance of valganciclovir for prophylaxis in high-risk OLT patients. Liver Transpl 15:963-967, 2009. (c) 2009 AASLD.

Gastric acid and particulate aspiration injury inhibits pulmonary bacterial clearance.

OBJECTIVE: To establish a model of secondary bacterial pneumonia following gastric aspiration and to identify possible mechanisms involved in the suppressed antibacterial defenses following the initial pulmonary insult. DESIGN: A controlled, in vivo laboratory study. SETTING: Research laboratory of a health sciences university. SUBJECTS: Ninety-five Long-Evans rats. INTERVENTIONS: Animals were anesthetized for neck dissection and placement of a 14-gauge catheter in the trachea. Gastric aspirate (1.2 mL/kg of saline, pH 1.25, and 40 mg/mL sterile rat gastric particles) or an equal amount of normal saline (pH 5.3) was instilled intratracheally. One minute after this insult, animals received an intratracheal instillation of either 5.6 x 10 colony-forming units of Escherichia coli or an equal volume of normal saline. The animals remained in room air until kill at 4 hrs or 24 hrs after the intratracheal instillation. The lungs were homogenized for quantitative bacterial cultures. Bronchoalveolar lavage fluid was obtained for cell counts and measurements of albumin, tumor necrosis factor-alpha, interleukin-1 beta, cytokine-induced neutrophil chemoattractant-1, macrophage inflammatory protein-2, monocyte chemoattractant protein-1, and interleukin 10. MEASUREMENTS AND MAIN RESULTS: Animals that received gastric aspirate (followed by normal saline or E. coli) had increased injury as assessed by significant reductions in oxygenation and elevations in bronchoalveolar lavage albumin. At 24 hrs, animals that received gastric aspirate inoculation followed by E. coli had significantly higher pulmonary bacterial counts compared with animals that received E. coli alone. Gastric aspiration injury followed by bacterial inoculation also resulted in acute, but transient, increases in tumor necrosis factor-alpha, interleukin-1 beta, cytokine-induced neutrophil chemoattractant-1, and macrophage inflammatory protein-2 and more sustained elevations of monocyte chemoattractant protein-1 and interleukin-10. CONCLUSIONS: Lung injury increases and bacterial clearance decreases in this experimental model of E. coli pneumonia following gastric aspiration. Cytokine profiles suggest possible mechanisms for the impaired antibacterial host defense.