Can history and exam alone reliably predict pneumonia?

• any abnormality on pulmonary auscultation, and
• at least 2 of 3 signs and symptoms: (1) a self-report of fever >38°C, or fever in the past 48 hours, (2) dyspnea or cough (productive or nonproductive), (3) tachypnea, malaise, or confusion.

Patients coming to the Leiden University Medical Center as well as those seen on home visits were included. We excluded patients who were pregnant and patients who had diseases that could have made follow-up difficult—for instance, those with an advanced malignancy.

History and exam. An investigator (primarily AWG) visited the patients at home within 24 hours of diagnosis by their primary care physician. The investigator took a standard history and did a physical examination. Sputum samples, throat swabs, and blood samples were collected for microbiological analysis; blood was also taken for erythrocyte sedimentaion rate (ESR) and C-reactive protein (CRP). An investigator visited the patients again 10 to 14 days later, at which time she took a second blood sample. (The management of the illness remained the primary care physician’s responsibility. Information on patients, microbiological assays, and criteria for microbiological diagnosis are given in detail in an earlier study.¹⁵)

Chest radiographs. In accordance with the study protocol, chest radiographs (posteroanterior and lateral) were taken 5 to 7 days after the history and exam were taken, in 1 of 4 nearby hospitals. Local radiologists made the first assessment during routine daily practice. The radiologists were asked to assess the existence of a consolidation on the radiographs. This study’s radiologist (FEJAW), who was aware of the clinical details but not informed about the results of the first assessment, reviewed the radiographs systematically. In case of a discrepancy between the 2 assessments, a third radiologist (HMZ) was asked to judge. The aim was to reach consensus. If previous radiographs were available, they were used for comparison.

The finding of a consolidation was regarded as evidence of pneumonia and served as the reference standard.

Literature search

Prediction models for pneumonia from the literature were identified by searching Medline from 1966 to June 2003, supplemented by checking article references.

The search was limited to studies with adult patients. Prediction models needed to be:

• From original prospective studies into the accuracy or precision of history and exam in a general practice or ambulatory setting, with inclusion criteria comparable with our definition of LRTI
• Developed with the use of multivariate techniques
• Not focused on hospital admission, hospital-acquired pneumonia, pediatric pneumonia, specific pneumonia (eg, tuberculosis), or AIDS-related pneumonia.

The search revealed 5 papers that met our criteria, from which we obtained 6 prediction rules: Singal,⁸ Heckerling,¹⁰ Melbye,¹¹ González Ortiz,¹² Hopstaken I,⁵ and Hopstaken II.⁵ The signs and symptoms used for diagnosis as well as the regression equations of these rules are given in TABLE 1.

Two further prediction models, though considered in 2 other reviews (Metlay et al¹⁶ and Zaat et al¹⁷), were not applied. These were models by Diehr,⁷ whose inclusion criteria (patients with cough) did not fit our definition for LRTI, and Gennis et al,⁹ which had only a univariate analysis of variables in the prediction of pneumonia.

Statistical analysis

As the patients’ data were collected for a prospective study on causes of LRTI,¹⁵ it offered us the opportunity to apply these prediction rules to our data set. We analyzed the data with SPSS version 11.0 for Windows (SPSS, Inc, Chicago, Ill). The 6 models were applied on our data set.

For this purpose, the regression scores corresponding to the different models for each patient were computed. The regression scores were used to calculate receiver operating characteristic (ROC) curves with areas under the curve. Positive and negative predictive values of the models were calculated, with a predicted probability for pneumonia >50% (ie, score on the regression equation of 0) was used as a cutoff point.

Results

Pneumonia rates in our patients

A total of 145 patients with LRTI were included in the study.¹⁵ For 137, a chest radiograph was taken. From these radiographs, 129 could be reviewed and 8 were lost after the first assessment. The mean age of the patients was 50 years (standard deviation=14); 86 (53%) patients were female and 63 (49%) had comorbidity, predominantly cardiovascular or pulmonary diseases (6 had both).

Of these 129 patients, 26 were diagnosed (by chest radiograph) to have pneumonia. The mean time between onset of symptoms and chest x-ray was 14 days; the mean time between chest x-ray and inclusion in the study was 9 days. All patients but 1 were treated with antibiotics.