PNEUMONIA

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inside Symptoms and signs Over- and under-diagnosis Treating in and out of hospital Pneumonia in children The authors

PROFESSOR NIGEL STOCKS, professor and head, discipline of general practice; director, primary health care research evaluation and development program; director, Australian sentinel practices research network, school of population health and clinical practice; and assistant dean (student), medical school, faculty of health sciences, University of Adelaide, Australia.

Community-acquired

PNEUMONIA

Pneumonia — a disease of diversity THE clinical presentation of pneumonia depends on several factors. Traditionally the disease has been subdivided into lobar pneumonia and bronchopneumonia. Lobar pneumonias develop after inhalation of infectious agents into the alveoli, while a bronchopneumonia has usually been spread from bronchitis or represents a complica-

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tion of a viral infection. When whole lobes have been consolidated, the lobar pneumonias are particularly severe and grave hypoxia may develop. Bronchopneumonia may also be severe in small children or when a patient is weakened by old age or comorbidity. The aetiological agent can also

determine the course of an infection, with some bacteria tending to give rise to a more severe pneumonia than others, for example, through developing septic infections. By contrast, pneumonias caused by viruses tend to be milder. The classification of pneumonias is nowadays mainly based on the aetiological agent — they are diag-

nosed as pneumococcal pneumonia, mycoplasma pneumonia, legionella pneumonia, etc. The reason is obvious — the aetiology directs the choice of treatment. Pneumonias caused by Mycoplasma pneumoniae, Chlamydia pneumoniae and Legionella species have been called ‘atypical’ because

PROFESSOR HASSE MELBYE, professor of general practice, institute of community medicine, University of Tromso, Norway.

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How to Treat – community-acquired pneumonia from previous page

CAP versus HAP CAP is defined as pneumonia that is acquired outside hospital in a person who is not immunocompromised. The aetiological agent is most often Streptococcus pneumoniae. It is also the agent that causes the most severe illness.

in the antibiotic era there is less reason for a nihilistic therapeutic approach to pneumonia in the elderly, although there may be circumstances, with patient or carer consent, when aggressive treatment is not pursued.

Common causes of pneumonia

it was thought that their clinical presentation was different from pneumococcal disease. However, there is considerable overlap in signs and symptoms and more recently the emphasis laid on aetiology has led to the subdivision of pneumonias into community-acquired pneumonia (CAP) and hospital-acquired pneumonia (HAP). Pneumonias can also be caused by chemicals, radiotherapy and allergic mechanisms, but these are not covered in this article.

Streptococcus pneumoniae (pneumococci) — the most common cause of CAP and the most common agent in hospitalised patients. Often sudden onset with high fever. High mortality when not treated with antibiotics. ■ Haemophilus Influenzae — similar features to pneumococcal infection. Small children, elderly, and patients with COPD or chronic bronchitis are most frequently infected. ■ Mycoplasma pneumoniae — occurs in outbreaks, with an incubation period of 2-3 weeks. Fever headache and cough prominent. Chest signs may be minimal despite radiographic changes. ■ Chlamydia pneumoniae — similar features to mycoplasma infection but not as frequently in epidemics. ■ Legionella pneumophila — spread via water droplets (potable water and cooling towers), symptoms include diarrhoea, high fever, hyponatraemia. Relatively high mortality. ■

Sir William Osler ... regarded pneumonia as “the captain of the men of death”. Other frequent causes are M pneumoniae, C pneumoniae and Legionella species. In contrast, pneumonias acquired in hospital often arise after procedures involving the respiratory tract, such as anaesthesia and assisted respiration. Bacteria that are usually

of low virulence and seldom cause infection in healthy people may attack the lung tissue, as the host defences, including the cough reflex, are often poor. Aerobic Gram-negative bacteria such as Klebsiella pneumoniae and Pseudomonas aeruginosa are

common agents and some will be multi-resistant hospital pathogens.

“Captain of the men of death” Sir William Osler, famous for his medical textbook of 1892, regarded pneumonia as “the captain of the men

Incidence and mortality of pneumonia European data indicate that the annual incidence of CAP in the 18-39 age group is six per 1000, and in those aged >75 it is 34 per 1000. About 20% of patients require hospitalisation and, of these, 5-10% require admission to intensive care. The overall mortality from CAP is 5-10%. In Australia the average GP will see about two cases of CAP per 1000 population per year. This figure is similar to the situation in the US, with 267 per 100,000 population hospitalised with CAP in 1991 and an overall case fatality rate of 8.8%.

of death”, and a frequent cause of death among the elderly. The disease could, according to Osler, also be looked at as the old man’s friend, relieving him from a distressful end of life. He had no belief in the treatments of that time. Now

Symptoms and signs of pneumonia FEVER, cough and dyspnoea have been known as the symptoms of pneumonia since the days of Hippocrates. Chest pain is also often present in lobar pneumonia, and may be particularly strong when associated with pleuritis. However, in most pneumonias found in general practice, two or three of these four cardinal symptoms may be missing or less pronounced. This is particularly the case in pneumonia caused by viruses, C pneumoniae and M pneumoniae, in which the main symptom is a persistent dry cough. Sudden onset of symptoms with chills, or acute worsening of influenza or a common cold, may indicate a pneumonia caused by ‘typical’ bacteria, such as pneumococcal pneumonia. Cough may be missing in earlystage pneumococcal pneumonia and in patients with insufficient cough reflex (infants, sick elderly, patients with stroke or those impaired by

Symptoms and signs of pneumonia Symptoms ■ Shortness of breath ■ Cough ■ Chest pain (pleuritic) ■ Confusion ■ Rigors or night sweats

Some of the listed symptoms are not significantly more common in pneumonia than in other lower respiratory tract infections. This is the case for very annoying coughs, purulent sputum and wheezes.

Clinical signs

Signs ■ Fever >38ºC ■ Raised respiratory rate ■ Focal chest signs

alcoholism). Nausea or diarrhoea may sometimes be prominent symptoms, and fever may be absent in infants and the elderly. Unsteadiness, as a sign of lowered blood pressure, tachypnoea, and mental confusion, are severe symptoms that may indicate a need for hospitalisation. Table 1 shows how often common symptoms and findings occur in primary care patients with pneumonia, revealed by three clinical studies.

The typical signs are rapid breathing, dullness to percussion over an involved lung lobe, bronchial breathing and localised crackles heard on auscultation. Wheezes may also be heard, either as a sign of a concomitant bronchitis, or as a localised sign of narrowed bronchial branches or mucus plugs in the bronchial tree. However, in about half of patients with pneumonia diagnosed by CXR and encountered in general practice, none of these signs are found, and crackles may also be heard in acute bronchitis, COPD and heart failure. Unsteadiness and confusion can be seen in pneumonia among the elderly. Inattentiveness may be reported by an infant’s parents.

Table 1: Frequency (%) of common symptoms and findings in pneumonia in primary care, as found in three clinical studies Frequency (%) Symptom/finding Very annoying cough Dry cough Purulent sputum Dyspnoea Severe dyspnoea Chest pain Severe chest pain Chills Crackles (rales) Wheezes/rhonchi Dullness to percussion C-reactive protein >20mg/L C-reactive protein >40mg/L

1

Diehr, et al —

2

Melbye, et al 65

3

Hopstaken, et al —

— 65 — — — 17 31 19 15 4

40 35 85 35 60 35 80 35 15 14

38 59 72 — 66 — 69 32 71 —



85

79



55

60

1. Diehr P, et al. Prediction of pneumonia in outpatients with acute cough: a statistical approach. Journal of Chronic Disease 1984; 37:215-25. 2. Melbye H, et al. Diagnosis of pneumonia in adults in general practice. Scandinavian Journal of Primary Health Care 1992; 10:226-33. 3. Hopstaken RM, et al. Contributions of symptoms, signs, erythrocyte sedimentation rate, and C-reactive protein to a diagnosis of pneumonia in acute lower respiratory tract infection. British Journal of General Practice 2003; 5:358-64.

Diagnosis BECAUSE typical findings are frequently missing and the specificity of crackles is low, the diagnosis is seldom clearcut. Pneumonia can be overlooked when cough is the only symptom, and no abnormal chest signs can be found. This was shown in an American study of 1819 adults with acute cough. A CXR was ordered by the doctor in 272 cases, and a pneumonic infiltrate was found in 16 of the radiographs. CXR was later taken in the remaining 1547 patients, in whom the doctors had not suspected pneumonia, and a pneumonic infiltrate was diag-

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nosed in 32 of these. Over-diagnosis is frequently made when crackles are heard, while the lack of abnormal chest findings is a common reason for underdiagnosis.

All pneumonias diagnosed by CXRs were also seen on CT. You cannot always rely on a negative radiograph when deciding on antibiotic treatment. CXR should be ordered if the patient is severely ill and there is doubt about the diagnosis, and in cases with slow recovery. A follow-up CXR should be ordered after six weeks (the resolution of infiltrates may take this long) in patients with increased risk of lung cancer, ie, smokers older than 40-50.

Chest X-ray Although CXR is regarded as a diagnostic gold standard for pneumonia, you cannot rely on radiography in all cases. It is well known that radiologists not infrequently disagree in their interpretations. When plain CXR was compared with high-resolution CT in patients with suspected pneumonia, eight out of 26 pneumonias diagnosed by CT were not diagnosed by CXR.

| Australian Doctor | 16 March 2007

Urine tests for Legionella species are at present usually limited to hospitalised patients.

Microbiological testing In Australia, CAP is usually caused by one organism, most

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commonly S pneumoniae in Australia; other important causes include M pneumoniae, C pneumoniae and Legionella (see box, above). Although an aetiological agent can be sought, the choice of antibiotics is usually based on a presumptive diagnosis. PCR analysis and IgM tests may allow identification of some aetiological agents within a day or two, which makes it possible to guide a change of treatment if the patient shows no sign of improvement. However, PCR analysis of sputum or nasopharynx specimens are not always available.

Traditional culture of expectorated sputum is of limited value, except when looking for the tubercle bacillus. It takes several days to get an answer and cultures grown do not always represent the infectious agent. Rapid tests for agents such as M pneumoniae and Legionella species have been developed and may be available in routine general practice in the future. Legionella urinary antigen testing and blood cultures should be reserved for patients admitted to hospital. New tests using throat swabs and PCR are being developed.

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Over- and under-diagnosing pneumonia Consequences of overdiagnosing pneumonia MAKING a diagnosis of pneumonia implies prescribing of antibiotics. In many cases of over-diagnosis the patient actually has acute bronchitis or influenza and does not need antibacterial treatment. In some cases the patient experiences an exacerbation of COPD, and adequate antiasthma treatment may be neglected. Pneumonia may also be wrongly diagnosed in acute heart failure following MI and in pulmonary embolism.

Consequences of underdiagnosing pneumonia In most cases when the diag-

cations or death. Such cases sometimes appear on the front page of newspapers. It is worth remembering that in the pre-antibiotic age the mortality of patients with pneumonia (pneumococci on blood culture) was 90%.

nosis has been missed, the pneumonia is mild and the patient recovers without antimicrobial therapy. This will often be the case when the aetiological agent is a virus, C pneumoniae or M pneumoniae. In other cases of overlooked pneumonias not treated with antibiotics, the disease will deteriorate. The correct diagnosis will usually be made at a later stage, and soon enough for recovery, either spontaneously or after starting an appropriate antibiotic. In a few cases the misdiagnosed pneumonia will get rapidly worse, and antibiotics will not be given in time to avoid septic compli-

Point-of-care testing White blood cell count (WCC), erythrocyte sedimentation rate (ESR), and Creactive protein (CRP) tests may add valuable information. WCC is usually elevated in pneumococcal pneumonia but is usually normal in pneumonias caused by viruses, M pneumoniae and C pneumoniae. The ESR usually rises in

values between 10mg/L and 100mg/L, the duration of illness must be taken into account. In uncomplicated viral infections the CRP value usually peaks after 3-4 days of illness, and may reach 100mg/L in the most ‘severe’ cases, for example, in influenza. The CRP value then decreases rapidly and is usually 100mg/L can support a diagnosis of pneumonia, as can a persistently elevated value after one week of illness. CRP tests for use in GP surgeries give results within five minutes.

all pneumonias, regardless of aetiology, but it can take a few days before the value exceeds the reference range. The CRP test has shown to be of greatest value, particularly in assessing response to treatment. An elevated value is usually seen within 12 hours, and the extent of the increase reflects the severity of the disease. Most pneumonia patients admitted to hospital have CRP values >100mg/L. Pneumonia can usually be ruled out when CRP is 7mmol/L. ■ A respiratory rate ≥30 breaths/min. ■ A diastolic blood pressure 50 ■ History of neoplastic disease, congestive cardiac failure, cerebrovascular, renal or liver disease ■ Clinical signs — altered mental state, pulse rate ≥125 bpm, respiratory rate ≥30 breaths/min, systolic blood pressure

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