What is pneumonia?

[Naveed Yaseen]

Pneumonia is an infection of one or both lungs which is usually caused by bacteria, viruses, or fungi. Prior to the discovery of antibiotics, one-third of all people who developed pneumonia subsequently died from the infection. Currently, over 3 million people develop pneumonia each year in the United States. Over a half a million of these people are admitted to a hospital for treatment. Although most of these people recover, approximately 5% will die from pneumonia. Pneumonia is the sixth leading cause of death in the United States.

How do people “catch pneumonia”?

Some cases of pneumonia are contracted by breathing in small droplets that contain the organisms that can cause pneumonia. These droplets get into the air when a person infected with these germs coughs or sneezes. In other cases, pneumonia is caused when bacteria or viruses that are normally present in the mouth, throat, or nose inadvertently enter the lung. During sleep, it is quite common for people to aspirate secretions from the mouth, throat, or nose. Normally, the body’s reflex response (coughing back up the secretions) and immune system will prevent the aspirated organisms from causing pneumonia. However, if a person is in a weakened condition from another illness, a severe pneumonia can develop. People with recent viral infections, lung disease, heart disease, and swallowing problems, as well as, drug users, and those who have suffered a stroke or seizure are at higher risk for developing pneumonia than the general population.

Once organisms enter the lungs, they usually settle in the air sacs of the lung where they rapidly grow in number. This area of the lung then becomes filled with fluid and pus as the body attempts to fight off the infection.

What are pneumonia symptoms and signs?

Most people who develop pneumonia initially have symptoms of a cold which are then followed by a high fever (sometimes as high as 104 degrees Fahrenheit), shaking chills, and a cough with sputum production. The sputum is usually discolored and sometimes bloody. People with pneumonia may become short of breath. The only pain fibers in the lung are on the surface of the lung, in the area known as the pleura. Chest pain may develop if the outer pleural aspects of the lung are involved. This pain is usually sharp and worsens when taking a deep breath, known as pleuritic pain.

In other cases of pneumonia, there can be a slow onset of symptoms. A worsening cough, headaches, and muscle aches may be the only symptoms. In some people with pneumonia, coughing is not a major symptom because the infection is located in areas of the lung away from the larger airways. At times, the individual’s skin color may change and become dusky or purplish (a condition known as “cyanosis”) due to their blood being poorly oxygenated.

Children and babies who develop pneumonia often do not have any specific signs of a chest infection but develop a fever, appear quite ill, and can become lethargic. Elderly people may also have few symptoms with pneumonia.

How is pneumonia diagnosed?

Pneumonia may be suspected when the doctor examines the patient and hears coarse breathing or crackling sounds when listening to a portion of the chest with a stethoscope. There may be wheezing, or the sounds of breathing may be faint in a particular area of the chest. A chest x-ray is usually ordered to confirm the diagnosis of pneumonia. The lungs have several segments referred to as lobes, usually two on the left and three on the right. When the pneumonia affects one of these lobes it is often referred to as lobar pneumonia. Some pneumonias have a more patchy distribution that does not involve specific lobes. In the past, when both lungs where involved in the infection, the term “double pneumonia” was used. This term is rarely used today.

Sputum samples can be collected and examined under the microscope. If the pneumonia is caused by bacteria or fungi, the organisms can often be detected by this examination. A sample of the sputum can be grown in special incubators, and the offending organism can be subsequently identified. It is important to understand that the sputum specimen must contain little saliva from the mouth and be delivered to the laboratory fairly quickly. Otherwise, overgrowth of noninfecting bacteria may predominate.

A blood test that measures white blood cell count (WBC) may be performed. An individual’s white blood cell count can often give a hint as to the severity of the pneumonia and whether it is caused by bacteria or a virus. An increased number of neutrophils, one type of WBC, is seen in bacterial infections, whereas an increase in lymphocytes, another type of WBC, is seen in viral infections.

Bronchoscopy is a procedure in which a thin, flexible, lighted viewing tube is inserted into the nose or mouth after a local anesthetic is administered. The breathing passages can then be directly examined by the doctor, and specimens from the infected part of the lung can be obtained.

Sometimes, fluid collects in the pleural space around the lung as a result of the inflammation from pneumonia. This fluid is called a pleural effusion. If the amount of this fluid that develops is large enough, it can be removed by inserting a needle into the chest cavity and withdrawing the fluid with a syringe in a procedure called a thoracentesis. In some cases, this fluid can become severely inflamed (parapneumonic effusion) or infected (empyema) and may need to be removed by more aggressive surgical procedures.

What are some of the organisms that cause pneumonia, and how are they treated?

The most common cause of a bacterial pneumonia is Streptococcus pneumoniae. In this form of pneumonia, there is usually an abrupt onset of the illness with shaking chills, fever, and production of a rust-colored sputum. The infection spreads into the blood in 20%-30% of cases, and if this occurs, 20%-30% of these patients die.

Two vaccines are available to prevent pneumococcal disease; the pneumococcal conjugate vaccine (PCV7; Prevnar) and the pneumococcal polysaccharide vaccine (PPV23; Pneumovax). The pneumococcal conjugate vaccine is part of the routine infant immunization schedule in the U.S. and is recommended for all children < 2 years of age and children 2-4 years of age who have certain medical conditions. The pneumococcal polysaccharide vaccine is recommended for adults at increased risk for developing pneumococcal pneumonia including the elderly, people who have diabetes, chronic heart, lung, or kidney disease, those with, cigarette smokers, and in those people who have had their spleen removed.

Antibiotics often used in the treatment of this type of pneumonia include penicillin, amoxicillin and clavulanic acid (Augmentin, Augmentin XR), and macrolide antibiotics including erythromycin, azithromycin (Zithromax, Zmax), and clarithromycin (Biaxin). Penicillin was formerly the antibiotic of choice in treating this infection. With the advent and widespread use of broader-spectrum antibiotics, significant drug resistance has developed. Penicillin may still be effective in treatment of pneumococcal pneumonia, but it should only be used after cultures of the bacteria confirm their sensitivity to this antibiotic.

Klebsiella pneumoniae and Hemophilus influenzae are bacteria that often cause pneumonia in people suffering from chronic obstructive pulmonary disease (COPD). Useful antibiotics in this case are the second- and third-generation cephalosporins, amoxicillin and clavulanic acid, fluoroquinolones (levofloxacin [Levaquin], moxifloxacin-oral [Avelox], gatifloxacin-oral [Tequin], and sulfamethoxazole and trimethoprim [Bactrim, Septra]).

Mycoplasma pneumoniae is a type of bacteria that often causes a slowly developing infection. Symptoms include fever, chills, muscle aches, diarrhea, and rash. This bacterium is the principal cause of many pneumonias in the summer and fall months, and the condition often referred to as “atypical pneumonia.” Macrolides (erythromycin, clarithromycin, azithromycin, and fluoroquinolones) are antibiotics commonly prescribed to treat Mycoplasma pneumonia.

Legionnaire’s disease is caused by the bacterium Legionella pneumoniae that is most often found in contaminated water supplies and air conditioners. It is a potentially fatal infection if not accurately diagnosed. Pneumonia is part of the overall infection, and symptoms include high fever, a relatively slow heart rate, diarrhea, nausea, vomiting, and chest pain. Older men, smokers, and people whose immune systems are suppressed are at higher risk of developing Legionnaire’s disease. Fluoroquinolones are the treatment of choice in this infection. This infection is often diagnosed by a special urine test looking for specific antibodies to the specific organism.

Mycoplasma, Legionnaire’s, and another infection, Chlamydia pneumoniae, all cause a syndrome known as “atypical pneumonia.” In this syndrome, the chest x-ray shows diffuse abnormalities, yet the patient does not appear severely ill. These infections are very difficult to distinguish clinically and often require laboratory evidence for confirmation.

Pneumocystis carinii pneumonia is another form of pneumonia that usually involves both lungs. It is seen in patients with a compromised immune system, either from chemotherapy for cancer, HIV/AIDS, and those treated with TNF (tumor necrosis factor), such as for rheumatoid arthritis. Once diagnosed, it usually responds well to sulfa-containing antibiotics. Steroids are often additionally used in more severe cases.

Viral pneumonias do not typically respond to antibiotic treatment. These infections can be caused by adenoviruses, rhinovirus, influenza virus (flu), respiratory syncytial virus (RSV), and parainfluenza virus (that also causes croup). These pneumonias usually resolve over time with the body’s immune system fighting off the infection. It is important to make sure that a bacterial pneumonia does not secondarily develop. If it does, then the bacterial pneumonia is treated with appropriate antibiotics. In some situations, antiviral therapy is helpful in treating these conditions.

Fungal infections that can lead to pneumonia include histoplasmosis, coccidiomycosis, blastomycosis, aspergillosis, and cryptococcosis. These are responsible for a relatively small percentage of pneumonias in the United States. Each fungus has specific antibiotic treatments, among which are amphotericin B, fluconazole (Diflucan), penicillin, and sulfonamides.

Conclusions: Pneumonia can be a serious and life-threatening infection. This is true especially in the elderly, children, and those that have other serious medical problems, such as COPD, heart disease, diabetes, and certain cancers. Fortunately, with the discovery of many potent antibiotics, most cases of pneumonia can be successfully treated. In fact, pneumonia can usually be treated with oral antibiotics without the need for hospitalization.

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