Reviews

The Value and Complications of Percutaneous Transthoracic Lung Aspiration for the Etiologic Diagnosis of Community-Acquired Pneumonia

Pneumonia is an important cause of morbidity and mortality globally. It is the leading cause of death in infants and young children with the majority of these deaths occurring in low income countries. Risk factors affecting incidence and outcome include extremes of age, poor nutrition, immunosuppression, environmental exposures and socioeconomic determinants. Pneumonia can be caused by a wide range of pathogens including bacteria, viruses and fungi, and the etiology varies by epidemiological setting, comorbidities and whether the pneumonia is community-acquired or hospital-acquired. Streptococcus pneumoniae is the major cause of community-acquired bacterial pneumonia while Gram negative bacteria, often resistant to multiple antibiotics, are common causes of hospital-acquired pneumonia and pneumonia in immunosuppressed individuals. Diagnosis is generally clinical and management is based mainly on knowledge of likely causative pathogens as well as clinical severity and presence of known risk factors. Timely and effective antibiotic treatment and oxygen therapy if hypoxemic are critical to patient outcomes. Preventive measures range from improved nutrition and hygiene to specific vaccines that target common causes in children and adults such as the pneumococcal or influenza vaccines.

To investigate the safety and practicability of conducting transthoracic fine-needle aspiration (TFNA) in a general hospital setting, we applied the TFNA procedure to 20 patients hospitalized with community-acquired pneumonia (CAP) within 36 h of admission. Also, a preliminary assessment was made of the potential value of adding TFNA to conventional methods of diagnostic microbiology. TFNA was easy to perform and caused little discomfort, and no serious adverse events were observed. In spite of ongoing antimicrobial treatment, a likely aetiological diagnosis was established for 14 of 20 (70%) of the patients. TFNA may provide important additional information on the aetiology of CAP.

The pneumolysin (ply) gene is widely used as a target in PCR assays for Streptococcus pneumoniae in respiratory secretions. However, false-positive results with conventional ply-based PCR have been reported. The aim here was to study the performance of a quantitative ply-based PCR for the identification of pneumococcal lower respiratory tract infection (LRTI). In a prospective study, fibreoptic bronchoscopy was performed in 156 hospitalized adult patients with LRTI and 31 controls who underwent bronchoscopy because of suspicion of malignancy. Among the LRTI patients and controls, the quantitative ply-based PCR applied to bronchoalveolar lavage (BAL) fluid was positive at ≥10³ genome copies/mL in 61% and 71% of the subjects, at ≥10⁵ genome copies/mL in 40% and 58% of the subjects, and at ≥10⁷ genome copies/mL in 15% and 3.2% of the subjects, respectively. Using BAL fluid culture, blood culture, and/or a urinary antigen test, S. pneumoniae was identified in 19 LRTI patients. As compared with these diagnostic methods used in combination, quantitative ply-based PCR showed sensitivities and specificities of 89% and 43% at a cut-off of 10³ genome copies/mL, of 84% and 66% at a cut-off of 10⁵ genome copies/mL, and of 53% and 90% at a cut-off of 10⁷ genome copies/mL, respectively. In conclusion, a high cut-off with the quantitative ply-based PCR was required to reach acceptable specificity. However, as a high cut-off resulted in low sensitivity, quantitative ply-based PCR does not appear to be clinically useful. Quantitative PCR methods for S. pneumoniae using alternative gene targets should be evaluated.

HIV infection is a major risk factor for death in childhood pneumonia in HIV-endemic regions. Improved case management and preventive strategies require better understanding of the impact of HIV on causes, clinical presentation, and outcome.

A prospective, clinical descriptive study of Malawian infants and children with severe pneumonia included blood culture and nasopharyngeal aspiration for diagnosis of pneumocystis pneumonia (PcP). A select group with consolidation on chest radiograph, and without severe hypoxia or hyperinflation, also had lung aspirate taken for culture and identification of bacterial deoxyribonucleic acid by real-time polymerase chain reaction (PCR).

There were 327 study patients with a median age of 11 months (range, 2 months–14 years). HIV prevalence was 51%. There were 58 cases of confirmed bacterial pneumonia, of which the most common bacterial isolates were Streptococcus pneumoniae and Salmonella typhimurium. Of the 54 lung aspirates, only 2 were positive on culture but 27 were positive for bacterial deoxyribonucleic acid by PCR. PcP was confirmed in 16 patients, and was associated with young age, severe hypoxia, HIV infection, and a very poor outcome. The overall case-fatality rate was 10% despite presumptive therapy for PcP and routine broad-spectrum antibiotic treatment appropriate for local antimicrobial susceptibility data. Most of the deaths occurred in infants of 2 to 6 months of age and PcP was associated with 57% of these deaths.

PcP is a major barrier in reducing the case-fatality rate of severe pneumonia in infants of HIV-endemic communities. The use of PCR on lung aspirate specimens greatly increased the diagnostic yield.

Tracheal aspirates were collected from 176 hospitalized antibiotic-pretreated children with community-acquired pneumonia. Haemophilus influenzae and Streptococcus pneumoniae were detected by both culture and target-enriched multiplex (TEM)-PCR whereas Mycoplasma pneumoniae and Chlamydia pneumoniae were detected by TEM-PCR only. TEM-PCR detected more S. pneumoniae (32 vs. 7) and H. influenzae (29 vs. 23) than did culture. TEM-PCR detected an additional 26 M. pneumoniae and 1 C. pneumoniae. TEM-PCR significantly enhances the pathogen-specific diagnosis of CAP in children.