Making the Right Call With. Pneumonia. Community-acquired pneumonia (CAP) is a. Community-Acquired. What exactly is CAP?

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1 Making the Right Call With Community-Acquired Pneumonia In this article: By Thomas J. Marrie, MD The case of Allyson Allyson, 32, presented to the emergency department with a 48-hour history of anorexia, fever, chills, cough, and left pleuritic chest pain. Her history was significant for the use of intravenous acetaminophen and methylphenidate. On examination, she looked acutely ill (see Patient stats). Crackles were evident on auscultation over the left lung anteriorly. A chest radiograph was obtained (Figure 1). Patient stats Temperature: 39 C Blood pressure: 90/60 mmhg Respiratory rate: 28 breaths per minute Pulse: 110 beats per minute Oxygen saturation: 89% while breathing room air What does the chest radiograph show? What blood work would you order? What tests would you order to make an etiologic diagnosis? 1. What is community-acquired pneumonia? 2. What tests should be done to confirm diagnosis? Community-acquired pneumonia (CAP) is a common, and often serious, illness. It is the sixth leading cause of death in the U.S. and Canada and about 600,000 people are hospitalized with CAP each year. The overall mortality rate for patients with CAP ranges from 6% to 15%. 1,2 The key to the successful management of CAP is an accurate diagnosis of this illness. What exactly is CAP? CAP is an acute illness characterized by two or more of the symptoms and signs listed in Table 1. However, symptoms alone do not have a sufficient sensitivity and specificity to make a CAP diagnosis. Respiratory symptoms raise the possibility that a patient may have pneumonia and certain physical findings may heighten this suspicion. For example, a respiratory rate of 25 breaths per minute has a likelihood ratio of 1.5 to 3.4 for pneumonia, while the combination of heart rate < 96 The Canadian Journal of Diagnosis / August 2003

2 Table 1 Symptoms and signs of CAP CAP is characterized by two or more of the following symptoms: Fever Cough Sputum production Pleuritic chest pain Crackles Bronchial breathing New opacity on chest radiograph Figure 1. Chest radiograph showing a left upper lobe opacity and a rounded opacity in the right mid-lung field (nipple shadow). 100 beats per minute, temperature < 37.8 C, and a respiratory rate of < 20 breaths per minute reduces the probability of pneumonia. 3 How is CAP diagnosed? The chest radiograph is the gold standard for the diagnosis of CAP. When a lobar opacity is present in the setting of an acute respiratory illness, it is easy to arrive at a diagnosis of pneumonia. However, it is often not so easy to reach this conclusion in elderly persons who have radiographs of suboptimal quality. In this setting, inter- and intra-observer variability in the interpretation of chest radiographs of patients with possible pneumonia is well-documented. 4 Young and Marrie studied 15 patients with pneumonia and found that a panel of three radiologists agreed with the original radiologist on the diagnosis of pneumonia 87% of the time; conversely, when 21 internists read the same set of radiographs they agreed with the original radiologist only 72% of the time. 5 Thus, some patients with pneumonia don t get properly diagnosed. In a recent study, high resolution computed tomography (HRCT) scans of the chest and chest Family Tree Anti-inflammatory analgesic agent. Product Monograph available on request. General warnings for NSAIDs should be borne in mind. CELEBREX is a registered trademark of G.D. Searle & Co., used under permission by Pharmacia Canada Inc.

3 Table 2 Chest radiograph findings in patients with a clinical diagnosis of CAP made by a physician Finding Ambulatory patients Admitted patients Pneumonia 1,753 (41.2%) 1,845 (53.1%) Query pneumonia 544 (12.8%) 615 (17.7%) No pneumonia 1617 (38.0%) 928 (26.7%) Pleural effusion 324 (7.6%) 752 (21.6%) COPD 360 (8.5%) 618 (17.8%) COPD: Chronic obstructive pulmonary disease radiographs were simultaneously compared in 47 patients presenting with presumed CAP. The HRCT scans identified all 18 cases that were apparent on chest radiograph, as well as an additional eight cases. 6 Thus, eight out of 26 cases of the pneumonias in this study were not identified by chest radiography. 6 Table 2 gives the chest radiograph findings, as reported by a radiologist, in patients who had a clinical diagnosis of pneumonia and whose radiographs had been interpreted as positive for pneumonia. If your clinical suspicion of pneumonia is high, and the chest radiograph is reported as normal or no pneumonia, the simplest thing to do is to repeat the chest radiograph in 48 hours. Followup chest radiographs to document complete clearing of pneumonia are important in those who are over 45 and in patients who are Dr. Marrie is a professor, department of medicine, University of Alberta, and a staff member, Walter C. Mackenzie Health Sciences Centre, Edmonton, Alberta. Table 3 Tests for confirmed/suspected CAP Complete blood count Blood urea nitrogen Creatinine, glucose O 2 saturation Blood gas analysis in those with COPD or in those with an O 2 saturation 90% COPD: Chronic obstructive pulmonary disease O 2 : Oxygen tobacco smokers. The reason for this is that in patients who require admission to hospital for treatment of pneumonia, 2% will have lung cancer and their pneumonia is thus due to obstruction of a bronchus. In 50% of these cases, the radiologist suggests the diagnosis of malignancy, but often the malignancy is only discovered because the pneumonia fails to clear, triggering investigations, such as bronchoscopy. The rate of radiographic resolution of pneumonia is influenced by the age of the patient and underlying lung disease; patients with bacteremic 98 The Canadian Journal of Diagnosis / August 2003

4 pneumococcal pneumonia who are over 60 and have chronic obstructive pulmonary disease (COPD) require up to 12 weeks for resolution of pneumonia. The dilemma, then, is to determine the optimal timing of the followup chest radiograph among patients who are clinically well. In elderly patients with COPD, it is reasonable to wait eight to 12 weeks before doing the followup chest radiograph. How can diagnosis be confirmed? For patients who are seen in an office practice and who are well enough to be treated at home, no blood work or etiologic investigations are necessary. However, for patients who are seen in the ED, and for those who are ill enough to be admitted to hospital, certain tests should be performed (Table 3). These tests are important in the risk stratification of patients with CAP. Fine et al. assigned points to 20 different items to derive a pneumonia specific severity of illness score. 5 This system allowed categorization of patients with pneumonia into five strata, with increasing risk for mortality from risk class I to V. This scoring system can be used to help with the site of treatment decision. Patients in risk classes I and II can usually be treated at home; those in risk class III may require a period of observation in the ED before a decision is made about optimal site of treatment. Blood cultures are recommended as part of the diagnostic workup for patients with CAP who are admitted to hospital for treatment and the positivity rate is approximately 11%. 7,8 The recently published American Thoracic Society guidelines for the management of adults with CAP do not mention blood cultures as part of the recommended testing for patients with CAP managed out of hospital. 6 The Canadian Infectious Diseases Society and the Canadian Thoracic Society expert panel indicated that the precise incidence of bacteremia in patients with CAP managed on an ambulatory basis is unknown, but that it is lower than that in patients who require admission to hospital for treatment of CAP. 7 Likewise, the Infectious Diseases Society of America guidelines for the management of CAP in adults do not indicate that blood cultures should be part of the workup of patients with CAP being managed on an ambulatory basis. 8 How do you determine the cause of pneumonia? A gram stain of a proper sputum specimen (more than 10 squamous epithelial cells per low power microscopic field and more than 25 white blood cells per low power microscopic field) can be very valuable in making a rapid etiologic diagnosis. If large numbers of gram positive diplococci are seen, it is likely that the patient has pneumococcal pneumonia. The

5 Table 4 Tests available to determine cause of pneumonia Acid fast stain of sputum Important in the diagnosis of pulmonary tuberculosis Staining sputum with a fluorescein tagged monoclonal antibody directed against a pneumocystis antigen can be diagnostic for pneumocystis pneumonia Special stains for fungi can be important in the diagnosis of pneumonia due to blastomyces dermatitdis Nasopharyngeal swabs For viral culture or as a method of obtaining material for amplication of deoxyribonucleic acid of a microorganism Recently, patients with severe acute respiratory syndrome had these tests done and from these specimens, as well as from pulmonary tissue, a coronavirus was isolated. Enzyme immunoassay Recommended for patients with progressive pneumonia with risk factors for Legionnaires disease (such as exposure to an aquatic source for Legionella or recent travel) Streptococcus pneumoniae (S. pneumoniae) urinary antigen test Enzyme immunoassay, with results available in 15 minutes Sensitivity of 80% and specificity of % when bacteremic pneumococcal pneumonia is used as the gold standard Antigen may be detected for up to 1 month following onset of pneumonia In children, nasopharyngeal carriage of S. pneumoniae can result in a positive urinary antigen test The role of pneumococcal urinary antigen in the etiologic diagnosis of CAP is not clear at present What would I do? Based on recent experience with almost 8,000 patients with pneumonia who presented to EDs in Edmonton, my recommendation is to perform blood cultures in all those with pneumonia who have a temperature < 36 C or > 38.5 C, in patients with diabetes, and in those with chronic renal failure who are receiving hemodialysis. In addition, all patients who are going to be admitted should have blood cultures. gram stain may be the first clue to an unusual microorganism, such as Nocardia species or Actinomyces species, as the cause of the pneumonia. The gram stain is also important in the interpretation of sputum culture results. Growth of Escherichia coli (E. coli) or other aerobic gram negative bacilli from sputum, which on gram stain showed no gram negative bacilli, suggests that the E. coli is likely a contaminant. Some other etiologic tests are listed in Table 4. D x References 1. National Centre for Health Statistics, National hospital discharge survey: Annual summary 1990; Vital statistics 1992;13: Metlay JP, Fine MJL: Testing strategies in the initial management of patients with community-acquired pneumonia. Ann Intern Med 2003; 138(2): Surf your way to The American Thoracic Society: 2. The Canadian Thoracic Society: 3. InfectNet (maintained by the Canadian Infectious Disease Society): The Canadian Journal of Diagnosis / August 2003

6 Take-home message Diagnosis Chest radiograph is the gold standard for the diagnosis of CAP. Many pneumonias go undetected in a radiograph, therefore, if suspicion of pneumonia is high and the radiograph is normal, the best thing to do is to repeat the radiograph in 48 hours. Determining the time of followup radiographs is critical. It is important to determine the cause of pneumonia. The tests that can be used include: blood cultures, gram staining of proper sputum specimen, acid fast stain of sputum, nasopharyngeal swabs, enzyme immunoassay, and S. pneumoniae urinary antigen test. 4. Young M, Marrie TJ: Interobserver variability in the interpretation of chest roentgenograms of patients with possible pneumonia. Arch Intern Med 1994; 154(23): Fine MJ, Auble TE, Yealy DM, et al: A prediction rule to identify low-risk patients with communityacquired pneumonia. N Engl J Med 1997; 336(4): Syrjala H, Broas M, Suramo I, et al: High-resolution computed tomography for the diagnosis of community-acquired pneumonia. Clin Infect Dis 1998; 27(2): Mandell LA, Marrie TJ, Grossman RF, et al for the Canadian Community-Acquired Pneumonia Working Group: Canadian guidelines for the initial management of community-acquired pneumonia: An evidence based update by the Canadian Infectious Diseases Society and the Canadian Thoracic Society. Clin Infect Dis 2000; 31(2); Niederman MS, Mandell LA, Anzeuto A, et al: Guidelines for the management of adults with community-acquired pneumonia: Diagnosis, assessment of severity, antimicrobial therapy and prevention.am J Respir Crit Care Med 2001; 163(7): Sturmann KM, Bopp J, Molinari D, et al: Blood cultures in adult patients released from am urban emergency department: A 15-month experience. Acad Emerg Med 1996; 3(8): Bartlett JG, Dowell SF, Mandell LA, et al: Practice guidelines for the management of communityacquired pneumonia in adults. Clin Infect Dis 2000; 31(8): Look toward the future with full remission See page 72 For a quick-take on this article, go to our Frequently Asked Questions department on page 31.