Limited Value of Routine Microbiological Diagnostics in Patients Hospitalized for Community-acquired Pneumonia

Abstract

Current guidelines recommend microbiological diagnostic procedures as a part of the management of patients hospitalized for community-acquired pneumonia (CAP), but the value of such efforts has been questioned. Patients hospitalized for CAP were studied retrospectively, focusing on the use of aetiological diagnostic methods and their clinical impact. Adult patients, without known human immunodeficiency virus infection, admitted to hospital for CAP during 12 months, were evaluated with regard to the importance of aetiological diagnosis for tailoring antibiotic therapy, antibiotic-associated diarrhoea, Clostridium difficile disease, length of hospital stay and mortality. Of the 605 studied patients, 482 (80%) were subjected to Mycoplasma pneumoniae and/or respiratory virus serology and/or cultures of blood and/or sputum. They had a better prognosis than patients not subjected to microbiological diagnostics (mortality within 3 months was 9% vs 24%, p = 0.001), apparently reflecting differences in general health (e.g. less dementia diagnosis) but not the outcome of diagnostics. A presumptive aetiology was obtained only in 132 of the 482 patients, Streptococcus pneumoniae and M. pneumoniae being the most common agents (in 49 and 36 patients, respectively). Establishing an aetiological diagnosis had no impact on the number of in-hospital changes of therapy, on the proportion of new regimens having a narrower antimicrobial spectrum than the initial one or on the outcome. Therapy was changed to a drug directed specifically against the identified pathogen in only 16 out of these 132 patients and again without any overall improvement in the outcome variables. In a setting with a low frequency of antibiotic-resistant respiratory tract pathogens current routine microbiological diagnostics were found to be of limited value for the clinical management of patients hospitalized for CAP. Improved diagnostics in CAP are urgently needed, as establishing an aetiological diagnosis carries a potential for optimizing the antibiotic therapy.

Usefulness of aetiological tests for guiding antibiotic therapy in community-acquired pneumonia

“…Among CAP patients with an identified aetiological agent, therapy changes were carried out according to these findings in 12% in a study by Lidman et al [13] and in 32% in a study by Ewig et al [78]. In a study of patients with severe CAP [79], the results of microbiological investigations led to a change in therapy in 42% of cases.…”

“…In patients with non-severe CAP, overuse of broadspectrum antibiotics can increase the risk of adverse events [12,13] and the development of antibiotic resistance among respiratory pathogens [14] and other bacterial species [15]. Thus, for patients with non-severe CAP, the guidelines from the British Thoracic Society (BTS) [7] and the Swedish Society of Infectious Diseases [8] recommend monotherapy with penicillin or an aminopenicillin, unless atypical pathogens are suspected.…”

“…Sputum culture is often used for the identification of probable/presumed aetiologies in CAP [11][12][13]21,27], either singly [13,21] or with the simultaneous identification of the compatible organism in sputum Gram stain [11,12,27]. It is usually recommended that the quality of the sputum samples should be determined by microscopy [4,8].…”

Improving the use of sputum cultures in lower respiratory tract infection

“…15 In general our findings are supportive of literature showing that sputum samples have little overall impact upon practical management of patients. [2][3][4]16,17 Prior to our intervention approximately 13% of sputum samples (45/347) appeared to lead to a change in management, but half of these samples were 'inappropriate'. Even fewer samples (around 3%, 4/133) directly altered prescribing after the intervention.…”

Swedish guidelines for the management of community-acquired pneumonia in immunocompetent adults

“…The 3-month mortality was 12% in 1 study [16] [18,29] and Legionella spp. [17 Á/ 19,26,30], although outbreaks with C. pneumoniae [31] and Legionella spp.…”