Pneumonia

Pneumonia is an inflammation in the interstitium of the lung or alveoli caused by microorganisms. It is one of the most common causes of death due to infectious disease.

The most common organism that causes pneumonia is Streptococcus pneumoniae, treatment should be selected considering this pathogen. S pneumoniae typically lives pharynx and is carried by about 50 percent of the population.

This section will focus primarily on community-acquired pneumonia (CAP)

Risk Factors

Certain factors increase the risk of getting pneumonia. In addition, specific patients are more prone to specific types of pneumonia. Older patients are more likely to get pneumonia than their younger counterpart.

Those with chronic obstructive pulmonary disease (COPD) are more likely to get pneumonia and Haemophilus pneumoniae is most common in this group. Those who abuse alcohol are most likely to come down with Klebsiella pneumoniae. Younger adults who come down with pneumonia are more likely to be afflicted with an atypical organism such as Mycoplasma pneumoniae or Chlamydia pneumoniae. C. pneumoniae is responsible for 2-5% of all CAP pneumonia. Those who are exposed to air-conditioning or aerosolized water are most likely to be afflicted with Legionella pneumoniae. Children under the age of two are most likely to get pneumonia from viruses. Diabetics – especially if diabetic ketoacidosis is present – are more likely to be afflicted with Streptococcus pneumoniae or Staphylococcus aureus. HIV infections increases the risk of many unusually pneumonias. Signs and Symptoms

A good history will help the clinician determine which type of organism is likely affecting the patient. Signs and symptoms can be variable depending on the severity and the organism affecting the patient. The disease often starts with the onset of productive cough or purulent sputum, shortness of breath, tachycardia, pleuritic chest pain, fever and chills. The symptoms come on over a 1 to 10 hour period.

The exam typically shows abnormal lung sounds including focal crackles over the area of consolidation. In addition, dullness to percussion may be noted or egophony.

Different organisms may have different presentations. Streptococcus pneumoniae is characterized by rigors, rust-colored sputum and pleuritic chest pain. Legionella pneumoniae presents with systemic systems such as diarrhea, hyonatremia and these patients typically have underlying cardiac or respiratory chronic disease. Green sputum may be indicative of Pseudomonas or Haemophilus. Foul smelling sputum suggests an anaerobic infection. Chlamydia pneumoniae presents with a long prodrome, sore throat and a hoarse voice. Klebsiella pneumoniae typically occurs in those with chronic illness and alcoholism and presents with currant jelly sputum.

Other symptoms that may be present include: headache, diarrhea, nausea, vomiting and malaise, which are more common with atypical organisms.

Travel history or location of the patient also helps gives clues to the type of pneumonia. Blastomyces dermatitidis is more common in the Midwest United States, Coccidioides immitis is more common in the Southwest United States.

Animals can pass on certain types of infections. Exposure to cattle, goats or sheep may increase the risk Coxiella burnetii. Chlamydia psittaci transmission can occur with contact to ducks, chickens or turkeys. More uncommon causes of atypical pneumonia also present with atypical signs or symptoms. This includes tularemia where the patient had close contact with a deer or rabbit or was bitten by a tick or deer fly. Q fever may occur if there is close contact with a sheep or parturient cat. Psittacosis is caused by an organism form a psittacine bird. These patients may present with headache, myalgia, rash, pharyngitis, relative bradycardia, splenomegaly or cardiac involvement.

Many disease states increase the risk of certain types of pneumonias. Once a complete history is taken a physical exam can help in the diagnosis and treatment of pneumonia. Common findings include:

• Fever
• Tachycardia
• Bradycardia
• Increased respiratory rate
• Cyanosis
• Abnormal lung sounds: rales/crackles
• Altered mental status
• Dullness to percussion over lung consolidation

Other findings on the exam can help the clinician determine the etiology of the infection. Bullous myringitis indicates possible Mycoplasma pneumoniae. Aspiration pneumonia is indicated by a patient without a gag reflex, recent seizure activity or change in mental status. Significant periodontal disease with foul smelling sputum indicates possible anaerobic pneumonia.

Diagnosis

Most cases of pneumonia are diagnosed on clinical exam with a confirmatory chest x-ray. Different type of infections can appear differently on x-ray. Streptococcus pneumonia may show segmental or lobar opacity, possibly with air bronchogram. Focal opacity is seen in many different types of pneumonias. Klebsiella often affects the upper lungs while Legionella affects the lower lungs. Staphylococcus aureus as well as gram negative infections and anaerobic infections may present with cavitation and pleural effusion. M pneumoniae may present with an interstitial pattern.

Some patients may have a clear chest x-ray, but pneumonia is still suspected due to the patient’s clinical appearance. In this situation the use of a CAT scan may help diagnose pneumonia.

Blood work is done in more severe cases. A complete blood count will often show an elevated white blood cell count with a left shift. Leukopenia is a poor prognostic sign and may indicate impending sepsis. When patients are extremely sick blood cultures may be performed, but do not have a high yield as they are positive in about 40% of the cases.

Some patients have a sputum culture. Sputum examination provides an accurate diagnosis in approximately 50% of patients. A good specimen will have fewer than 10 squamous epithelial cells and more than 25 WBCs per low-power field. In some neutropenic patients there may be less than 25 white blood cells per low-power field despite infection in the lower respiratory tract. When gram stain demonstrates a single organism pneumonia is likely as opposed to when multiple organisms are present, which likely represents a contaminated specimen.

Based on clinically history and exam it is important to determine which organism is most likely causing the infection. Identifying the likely organism is important as it can mean the difference between treatment failure and success.

Atypical pneumonia presents "atypically". Features may include a low grade fever, mild, non-productive cough with body aches and fatigue. The presentation can be very similar to a viral infection. Legionella is associated with high fever and shortness of breath. Organisms that make up the atypical class include: Mycoplasma pneumoniae (the most common cause), Chlamydia pneumoniae, Legionella and Moraxella. The atypical pneumonias are less common than typical pneumonias, harder to diagnose, and are resistant to some antibiotics – such as beta-lactams. Legionella is diagnosed with direct fluorescent antibody or indirect fluorescent antibody; unfortunately this test has a high rate of false negative tests. A urine antigen for Legionella can be used with good accuracy.

Blood work to detect immunoglobulin M antibodies aid in the diagnosis of Mycoplasma and Chlamydia pneumonia. Likewise serology is essential in diagnosing unusual causes of pneumonia such as brucellosis and Q fever.

Culture of the sputum is typically not helpful and in the complete blood count the white blood cell count may be only mildly elevated. The chest x-ray can be variable showing a unilateral lower infiltrate or diffuse infiltrates.

If pleural effusion – particularly a parapneumonic pleural effusion- is present, thorocentesis should ensue. The fluid should be cultured and gram stained. Diagnostic testing can help determine if there is a complicated or simple effusion.

In some cases arterial blood gases are drawn which can help determine the severity of the infection and the need for supplemental oxygen. ABGs are indicated in all patients with a pulse oximetry reading of less than 90% or any other signs of hypoxia.

In severe or complicated cases of pneumonia bronchoscopy is performed which can help attain cultures to more definitively determine the causative organism.

For outpatient CAP the use of diagnostic tests is recommended if it is going to change the treatment plan. For CAP patients who were admitted to the hospital for management, blood cultures are likely not helpful as they lead to antibiotic narrowing in between zero and three percent of patients.

Treatment

Ninety percent of those with bacterial pneumonia who receive empiric treatment will improve. The first factor to determine in the treatment of patients is where the patient is going to be treated: outpatient or inpatient. Young healthy patients without acute distress are safely treated as outpatients. Hospitalization is indicated for patients who are sicker. It is essential that the clinician consider other co-morbid conditions as well as the severity of the illness upon initial presentation when considering where to treat the patient. Those who have multi-lobular infection, neutropenia or poor host resistance may need hospitalization. Patients with altered mental status and abnormal vital signs may need inpatient management.

While these are general rules, there is a scoring system that has been developed. The patient is classified into one of four categories.

Category 1: Community acquired pneumonia (CAP), less than 60 years old, no major medical co-morbidities

Category 2: Community acquired pneumonia with medial co-morbidities and/or over the age of 60 – with mild disease – able to be treated out of the hospital

Category 3: CAP that necessitates the hospital

Category 4: CAP that necessitates the ICU.

Inpatient care is much more expensive, costing the health care system 25 times more than outpatient care. One method to determine who is a candidate to be admitted to the hospital is using the CURB-65 scale. This looks at five parameters of the patient and if 2 or more are positive then the patient should be admitted to the hospital. While this is easy to remember it is not well studied.

Table 2Mortality Rate based on CURB-65 Score

Patients with a score of 0 or one can be treated as outpatients those with 2 should be admitted to a general medical unit and those with a score greater than 3 should be admitted to the intensive care unit.

Another method often used in the PSI method. This places patients into 5 classes. Class 1 and 2 should be treated as outpatients, 3 should be treated with a short hospitalization or an observation stay, class 4 and five should be inpatients. This is less useful clinically as it requires evaluating 20 variables and is more difficult to use.

Certain factors, if present, necessitate hospitalization even if CURB-65 or PSI scores do not recommend hospitalization. These include: an arterial oxygen saturation of less than 90% or a partial pressure of oxygen less than 60 mm Hg, individuals who are excessively vomiting, have cognitive dysfunction, have severe mental illness, poor functional capacity, injection drug use or are unable to care for themselves at home.

When deciding to hospitalize the patient or not, it is important to consider other co-morbid factors. Pneumonia has the potential to exacerbate many other disease states such as COPD, heart failure, renal failure or diabetes.

Based on the most likely causative organism initial antibiotics should be prescribed. The most likely organisms in those patients with pneumonia who are younger than 60, without medical co-morbidities, who are going to be managed as outpatients are S pneumoniae, M pneumoniae, C pneumoniae, H influenzae, Legionella species and S aureus. Macrolide antibiotics are the first-line choice for antibiotics and a second choice is doxycycline.

Those individuals who are not sick enough to be admitted to the hospital, but have co-morbidity and are over the age of 60 have pneumonia most likely caused by: S pneumoniae, H influenzae, Aerobic gram-negative bacilli, S aureus, M catarrhalis, Legionella species or Mycoplasma.

For the patient with a co-morbidity such as chronic lung, liver, heart or renal disease, diabetes, alcoholism, asplenia, cancer or a condition that suppresses the immune system or if they have been on an antibiotic in the last 3 months should be treated with a respiratory quinolone or a beta-lactam (high dose amoxicillin, amoxicillin/clavulanate or a higher generation cephalosporin) and a macrolide (doxycycline as an alternative). Caution must be implemented in areas where there is a high degree of macrolide resistance and the use of a quinolone should be considered.

Recent research compared the use of levofloxacin 750 mg a day against ceftriaxone 1 gram plus azithromycin 500 mg a day in CAP. The levofloxacin group had a lower length of stay and a shorter period of time in which they required intravenous antibiotics. Another study compared levofloxacin 750 mg IV to moxifloxacin 400 mg IV and the levofloxacin resulted in a reduced length of stay, but no difference in the percent of complications.

One notable side effect of the quinolones is their risk of tendon rupture. It most commonly occurs in the Achilles tendon, but could occur in any tendon. This is more common in individuals over 60 years old and those on corticosteroids.

When micro aspiration is suspected the use of Beta-lactam/Beta-lactamase inhibitors, clindamycin or a carbapenem should be considered.

Patients sick enough to be admitted to the hospital could be afflicted with S pneumoniae, H influenzae, polymicrobial (including aerobic bacteria) infection, Aerobic gram-negative bacilli, Legionella species, S aureus, C pneumoniae, M pneumoniae or M catarrhalis. The first choice is a respiratory quinolone or a beta-lactam (ceftriaxone, cefotaxime, ampicillin) and a macrolide (with doxycycline as a back-up).

Atypical pneumonia is treated with antibiotics and supportive care. Medications from the macrolide class are commonly chosen as they cover Mycoplasma pneumonia and Legionella.

Supportive care includes: rest, analgesics/antipyretics, fluids and cough suppressants.

Certain factors dictate the need to hospitalize a patient. The following risk factors predict higher death rates and a more complicated course: older than 65 years old or co-morbid illness such as COPD, diabetes, heart failure, alcoholism, chronic liver disease, aspiration or post-splenectomy. Certain findings on physical exam also predict a worse outcome such as a respiratory rate greater than 30 breaths per minute or a temperature greater than 101 degrees Fahrenheit, blood pressure less than 90/60 mm Hg and altered mental status.