A new study in the European Respiratory Journal suggests that testing patients for the presence of fever, crackling in the lungs, high pulse and low blood oxygen levels could help clinicians diagnose pneumonia in patients with lower respiratory tract infections and thus avoid prescribing unnecessary antibiotics.
The results of the large prospective study showed that 86.1% of patients with a chest x-ray confirmed diagnosis of pneumonia had at least one of these four clinical symptoms, and the positive predictive value of having at least one was 20.2%. Patient characteristics, such as age and medical history, and other symptoms, including shortness of breath and sputum color, did not help clinicians decide who had pneumonia.
The researchers believe the findings could help reduce the prescription of antibiotics for lower respiratory tract infections, which are usually caused by viruses and do not require antibiotics.
Unnecessary prescribing for lower respiratory tract infections is widely believed to be a contributing factor to antibiotic resistance, but prescribing rates remain high in the UK and other industrialized countries. A 2014 study found that the top 10% prescribing GPs in the UK prescribed antibiotics in 69% of consultations for respiratory tract infections, while median practices prescribed antibiotics in 54% of consultations.
“Most patients with lower respiratory tract infection recover perfectly without antibiotics, but, at the moment, about 60% of patients get a prescription,” said lead author Michael Moore, BM, BS, Professor in primary health care research at the University of Southampton, said in a press release from the European Lung Foundation. “If the prescription of antibiotics were limited to people with one or more of these signs, it could lead to a substantial reduction in unnecessary prescriptions for this disease.”
Independent predictors of pneumonia
For the study, the researchers recruited 28,883 patients who had visited 5,222 UK medical practices from 2009 to 2013 with an acute cough attributed to a lower respiratory tract infection, collected data on their symptoms and followed them for 30 days after their first visit. A total of 720 of these patients underwent chest X-ray within the first 7 days and 115 (0.4%) were eventually diagnosed with pneumonia.
Although most patients referred for an X-ray were older, sicker, and more likely to be smokers, the researchers found that patient characteristics did not provide useful information for diagnosing pneumonia. Neither do many of the patient’s symptoms.
But the researchers identified four symptoms from a clinical examination that were helpful in diagnosis, with a temperature above 37.8°C (100°F; relative risk [RR], 2.65) being the strongest independent predictor of pneumonia, followed by a crackle in one or both lungs (RR, 1.82), a pulse over 100 beats per minute (RR, 1.90) and lower blood oxygen saturation greater than 95% (RR, 1.73). Ninety-nine of 115 patients with pneumonia had at least one of these symptoms.
When the researchers examined the sensitivity and specificity of the four independent predictors among the subset of patients who had been referred for an X-ray, they found that the highest sensitivity (83.5%) was achieved when all four were taken into account.
Moore and his colleagues say the benefit of these four factors is that they are all easily measurable clinical symptoms that clinicians routinely test for, with the exception of blood oxygen levels. Oxygen saturation can be easily measured with noninvasive devices called pulse oximeters, which are widely available but not routinely used.
The strengths of the study are its size and large generalizable cohort, which limit selection bias. But because the patients selected for a chest x-ray were only a small sample of the full cohort and were generally older and sicker, milder cases of pneumonia may have been missed.
November 22 Eur Respir J study
November 23 European Lung Foundation Press release