Laboratory Diagnosis of Lower Respiratory Tract Infections: Controversy and Conundrums

Lower respiratory tract infections are among the most common infectious diseases of humans worldwide. In the United States alone, pneumonia and influenza rank as the sixth leading cause of death (18). Changes in the characteristics of the population as it ages and the swelling numbers of patients with immunocompromising conditions have increased the number of individuals at risk. An expanded variety of emerging pathogens likewise provides challenges for the microbiology laboratory. Overtreatment of acute uncomplicated bronchitis, which is largely due to viruses, has led to unparalleled levels of multidrug resistance among invasive pathogens such as Streptococcous pneumoniae. Practice guidelines for a rational approach to the evaluation and treatment of patients with acute bronchitis have recently been published in an effort to decrease the overuse of antibiotics and as an attempt to prevent further increases in rates of resistance (8). The laboratory’s role here is very limited. The role of the microbiology laboratory in the diagnosis of community-acquired pneumonia (CAP) remains controversial. Limitations of diagnostic tests have led to the development of guidelines for empirical treatment approaches (2, 3). Less controversial is the need to establish an etiology in the hospitalized patient and the immunocompromised host with lower respiratory tract infection. This minireview addresses the major categories of lower respiratory tract infections, the most common etiologic agents, and the laboratory tests (and their limitations) available to diagnose them.