The Modern Diagnostic Approach to Community-Acquired Pneumonia in Adults

Abstract

Respiratory tract infections, the majority of which are community acquired, are among the leading causes of death worldwide and a leading indication for hospital admission. The burden of disease demonstrates a ?U?-shaped distribution, primarily affecting young children as the immune system matures, and older adults as the process of immunosenescence and accumulation of comorbidities leads to increased susceptibility to infection. Diagnosis of community-acquired pneumonia (CAP) is traditionally based on demonstration of a new infiltrate on a chest radiograph in a patient presenting with an acute respiratory illness or sepsis. Advances in diagnosis have been slow, and although there are increasing data on the value of computed tomography or lung ultrasound as more sensitive diagnostic methodologies, they are not widely used as initial diagnostic tests. There are a wide range of differential diagnoses and pneumonia ?mimics? which should be considered in patients presenting with CAP. Once the diagnosis of CAP has been made, identifying the causative microorganism is the next stage in the diagnostic process. Traditional culture-based approaches are relatively insensitive and achieve a positive diagnosis in only 30 to 70% of cases, even when rigorously applied. Urinary antigen tests, polymerase chain reaction assays, and even next-generation sequencing technologies have become available and are increasing the rates of positive diagnosis. In an era of increasing antimicrobial resistance, the accurate diagnosis of CAP and determining the causative pathogen are ever more important. Getting these both right is key in reducing both morbidity and mortality from CAP, and appropriate antimicrobial stewardship which is now an international healthcare priority.

New insights and antimicrobial stewardship opportunities in viral pneumonia: five lung ultrasound cases

“…Delayed treatment of bacterial pneumonia results in high mortality and morbidity; however, viral respiratory infections, including pneumonia, are increasingly recognized, and clinical investigation or x‑ray to distinguish them from bacterial pneumonia seems to be inappropriate [ 16 ].…”

“…Procalcitonin (PCT)-guided therapy may reduce antibiotic consumption while lowering mortality in respiratory infections [ 32 – 35 ]. In viral respiratory infections diagnosed by multiplex polymerase chain reaction (PCR), bacterial superinfection can be ruled out by a low PCT level [ 36 , 37 ]; however, conflicting data and low adherence to PCT-guided therapy has been shown in clinical practice [ 38 ] and the detection rate of PCR for virus infection can be low [ 16 , 36 ].…”

“…Lung ultrasound (LUS) [ 39 ] and computed tomography (CT) are more sensitive than X-ray films for the detection of the signs of pneumonia [ 16 ] and have been used to distinguish viral from bacterial pneumonia [ 40 , 41 ]. LUS is easy to learn [ 42 ], widely available, and has shown to be indicative of viral infection [ 43 , 44 ], as has CT even in the absence of positive PCR [ 45 ].…”

Atypical bacterial pneumonia in the HIV-infected population

“…Currently, the diagnosis of pneumonia is based on clinical features and X-ray. The etiological diagnosis, however, is based on empirical data, culture, serology, nucleic acid amplification techniques (NAAT), and bronchoscopy [ 5 , 14 ]. When choosing any of these diagnostics, a number of points must be considered.…”

“…Therefore, depending on the stage of HIV infection, serology may not be clinically useful [ 16 ]. Due to the low sensitivities of serology, NAAT (such as polymerase chain reaction [PCR]) is becoming the diagnostic tool of choice for rapid identification of atypical bacteria in respiratory samples of HIV-infected and uninfected individuals [ 14 , 17 , 18 ]. However, although NAAT is highly specific, sensitivity has been shown to vary depending on the patient sample being tested (e.g.…”