Data indicate that Streptococcus pneumoniae is the most common bacterial cause of pneumonia, making it an important target for health policy. However, the burden of pneumococcal disease is currently measured only through patients with invasive pneumococcal disease. While previous studies suggest that the urinary antigen test (UAT) for pneumococcus exhibits high sensitivity and specificity, comparisons of pneumococcal pneumonias diagnosed as invasive disease with pneumococcal pneumonias defined by UAT results are lacking.
Comparing Patients by Diagnostic Method
For a study published in Chest, Adrian Ceccato, MD, and colleagues aimed to compare the clinical characteristics and outcomes of pneumococcal pneumonias diagnosed as classical “invasive disease” with pneumococcal pneumonias defined by UAT. “UATs have high sensitivity and specificity and can be performed at the point of care,” says Dr. Ceccato. “In spite of these favorable properties, they have not been incorporated in estimations of pneumococcal disease burden.”
The prospective, observational study included consecutive patients with community-acquired pneumonia (CAP) who visited emergency departments in Barcelona, Spain between January 2000 and December 2014. Participants were adults with a CAP diagnosis confirmed by chest radiograph and consistent clinical manifestations (eg, fever, cough, sputum production, pleuritic chest pain). Pneumococcal etiology was confirmed by UAT or by blood or pleural fluid culture.
“We found that a high percentage of cases of confirmed pneumococcal pneumonia are diagnosed by UAT,” explains Dr. Ceccato. “When we compared patients with invasive pneumococcal pneumonia (IPP) with patients with noninvasive pneumococcal pneumonia (NIPP) diagnosed only by UAT, we found clinical and evolutionary differences, including a higher severity of the disease in the IPP group. However, neither IPP nor NIPP were independently associated with 30-day mortality.”
The researchers also found that patients with IPP had more ICU admissions, more complications (both pulmonary and extra pulmonary), longer hospital stays, and longer time to clinical stability (Table). However, the differences in terms of mortality were nonsignificant (7 days vs. 30 days). When assessing predictors of 30-day mortality, they found expected risk factors for patients with CAP: age older than 74 years, chronic liver disease, mechanical ventilation requirement, and acute renal failure.
“However, invasive pneumococcal disease was not a risk factor for 30-day mortality,” says Dr. Ceccato. “We think that the presence of a positive culture in a sterile fluid alone (invasive disease) is not sufficient to increase the risk for mortality. A dysregulated host response to infection may be influenced by underlying factors such as age or comorbidities, leading to higher mortality. Our group has shown that the presence of bacteremia in pneumococcal pneumonia is not a risk factor for mortality. However, recent data from our group have shown that patients with pneumococcal bacteremic pneumonia and higher bacterial load had worse outcomes. Higher bacterial load, underlying conditions and host response seem to be the key factors for determining the risk of mortality.”
Use Both Methods
The burden of pneumococcal disease in adults should be measured by considering the pneumococcal pneumonias defined by both methods—invasive pneumococcal pneumonia and positive urinary antigen test—says Dr. Ceccato. “Urinary detection is an easy-to-perform and inexpensive test that allows the diagnosis of pneumococcal pneumonia with a high sensitivity and specificity,” he adds. “Since these populations appear to be different, the burden of the disease should be reported independently.
It is important to measure the burden of the disease in order to conduct adequate health planning and to evaluate the effects of vaccination. Also, new UATs with additional technology can provide information about the pneumococcal serotype causing pneumonia.”
