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.

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 alcoholics, 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.

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.

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.

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 alcoholism, 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) or alcoholism. 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 much pneumonia 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.

Major concerns have developed in the medical community regarding the overuse of antibiotics. Most sore throats and upper respiratory infections are caused by viruses rather than bacteria. Though antibiotics are ineffective against viruses, they are often prescribed. This excessive use has resulted in a variety of bacteria that have become resistant to many antibiotics. These resistant organisms are commonly seen in hospitals and nursing homes. In fact, physicians must consider the location when prescribing antibiotics (community-acquired pneumonia, or CAP, versus hospital-acquired pneumonia, or HAP).

The more virulent organisms often come from the health-care environment, either the hospital or nursing homes. These organisms have been exposed to a variety of the strongest antibiotics that we have available. They tend to develop resistance to some of these antibiotics. These organisms are referred to as nosocomial bacteria and can cause what is known as nosocomial pneumonia when the lungs become infected.

Recently, one of these resistant organisms from the hospital has become quite common in the community. In some communities, up to 50% of Staph aureus infections are due to organisms resistant to the antibiotic methicillin. This organism is referred to as MRSA (methicillin-resistant Staph aureus) and requires special antibiotics when it causes infection. It can cause pneumonia but also frequently causes skin infections. In many hospitals, patients with this infection are placed in contact isolation. Their visitors are often asked to wear gloves, masks, and gowns. This is done to help prevent the spread of this bacteria to other surfaces where they can inadvertently contaminate whatever touches that surface. It is therefore very important to wash your hands thoroughly and frequently to limit further spread of this resistant organism.

Doctors use antibiotics to treat pneumonia caused by bacteria, the most common cause of the condition. The number of days you take antibiotics depends on your general health, how serious your pneumonia is, and the type of antibiotic you are taking.

Your doctor will choose your antibiotic based on a number of things, including your age, your symptoms and how severe they are, and whether you need to go to the hospital.
Although experts differ on their antibiotic recommendations, the first antibiotic used usually is one that works against a wide range of bacteria (broad-spectrum antibiotic). All antibiotics used have a high cure rate for pneumonia.

If you do not have to go to the hospital, your doctor may use any of the following antibiotics:
•    Macrolides, such as azithromycin, clarithromycin, and erythromycin.
•    Tetracyclines, such as doxycycline.
•    Fluoroquinolones, such as gemifloxacin, levofloxacin, and moxifloxacin.
If you have to go to the hospital, your doctor may use any of the above antibiotics. Other antibiotics that your doctor may use in this situation include:
•    Cephalosporins, such as ceftriaxone, cefotaxime, and cefepime.
•    Penicillins, such as amoxicillin and ampicillin.
•    Vancomycin.

Antibiotics usually work well with younger, otherwise healthy people who have strong immune systems. You most likely will see some improvement in symptoms in 2 to 3 days. Unless you get worse during this time, your doctor usually will not change your treatment for at least 3 days. If there is no improvement or if your symptoms get worse, you may need culture and sensitivity testing. These tests help identify the organism that is causing your symptoms. These tests also help your doctor find out whether the bacteria may be resistant to the antibiotic.

You likely will not have to go to the hospital unless you:
•    Are older than 65.
•    Have other health problems, such as chronic obstructive pulmonary disease, heart failure, asthma, diabetes, long-term (chronic) kidney failure, or chronic liver disease.
•    Cannot care for yourself or would not be able to tell anyone if your symptoms got worse.
•    Have severe illness with less oxygen getting to the tissues (hypoxia).
•    Have chest pain caused by inflammation of the lining of the lung (pleurisy) so you are not able to cough up mucus effectively and clear your lungs.
•    Are being treated outside a hospital and are not getting better (such as your shortness of breath not improving).
•    Are not able to eat or keep food down so you need to take fluids through a vein (intravenous).

Pneumonia also can be caused by viruses, such as those that cause influenza (flu) and chickenpox (varicella).

•    At this time, there is no proven medicine to treat pneumonia caused by the influenza virus. Home treatment, such as rest and taking care of your cough, is the only treatment.
•    Varicella pneumonia, which is rare, can be treated with antiviral medicine.

There are a number of steps you can take to help prevent getting pneumonia.

•    Stop smoking. Smoking makes it more likely you will get pneumonia.
•    Avoid contact with people who have respiratory tract infections, such as colds and influenza (flu). Pneumonia may develop after these types of infections.
•    If you have not had measles or chickenpox or gotten vaccines against these diseases, avoid contact with people who have these infections. Pneumonia can be a complication of measles or chickenpox, so getting these infections can put you at risk for getting pneumonia.
•    Wash your hands often. This helps prevent the spread of viruses and bacteria that may cause pneumonia.

Vaccinations
Vaccines to help prevent pneumonia are available. But research shows that they might not help everyone. The vaccine for children is called the pneumococcal conjugate vaccine (PCV).
Some studies show that the vaccine does not reduce the risk of pneumonia in adults. But the vaccine can prevent some of the serious complications of pneumonia, such as infection in the bloodstream (bacteremia) or throughout the body (septicemia), in younger adults and those older than 55 years with a healthy immune system.

Experts recommend the vaccine for people who are older than 65, for adults who smoke, and for people who have a long-lasting (chronic) condition that increases their risk of pneumonia.
Other vaccines can prevent common diseases in which pneumonia may be a complication.

•    Vaccination of children for measles can prevent most cases of measles. Adults may need to be vaccinated against measles if they have not had the disease or were not vaccinated during childhood.
•    Yearly vaccinations (shots) for influenza may prevent you from getting the flu. Influenza often can lead to pneumonia, especially in older adults or in people who have other long-term (chronic) medical diseases. The influenza vaccine can be given at the same time as the pneumococcal vaccine but in a different arm.
•    Vaccination with the chickenpox vaccine (varicella-zoster vaccine) can prevent most cases of pneumonia caused by the virus that causes chickenpox. Consider getting a vaccination if you are older than 13 and have not yet had chickenpox.
The mineral zinc may help reduce the risk of pneumonia in children. Zinc can be found in certain foods (lean red meats, seafood, beans, cereals) or added to the diet in supplements. Studies in developing countries found that the incidence of pneumonia in children dropped when zinc was added to the diet.8 Always talk to your doctor before giving your child zinc supplements or any other vitamin or mineral supplement.

Complications of pneumonia that may occur include buildup of fluid in the space between the lung and chest wall (pleural effusion), pockets of pus that form in the space between the lung and chest wall (empyema) or in the lung itself (lung abscess), secondary bacterial lung infection after a viral infection, secondary infection, such as a vaginal infection or infections of the digestive system, because of antibiotic therapy, bacteria in the bloodstream (bacteremia) or throughout the body (septicemia), infection caused by swelling of the covering of the spinal cord (meningitis), infection of a joint caused by spread of bacteria through the bloodstream (septic arthritis), and infection of the heart muscle or the sac surrounding the heart (endocarditis or pericarditis).

Abscesses in the lung are thick-walled, pus-filled cavities that are formed when infection has destroyed lung tissue. They are frequently a result of aspiration pneumonia if a mixture of organisms is carried into the lung. Abscesses can cause hemorrhage (bleeding) in the lung if untreated, but antibiotics that target them have significantly reduced their danger. Abscesses are more common with Staphylococcus aureus or Klebsiella pneumoniae, and uncommon with Streptococcus pneumoniae. Respiratory failure is one of the important causes of death in patients with pneumococcal pneumonia. Acute respiratory distress syndrome (ARDS) is the specific condition that occurs when the lungs are unable to function and oxygen is so severely reduced that the patient's life is at risk. Failure can occur if pneumonia leads to mechanical changes in the lungs (called ventilatory failure) or oxygen loss in the arteries (called hypoxemic respiratory failure). Bacteremia (bacteria in the blood) is the most common complication of pneumococcus infection, but rarely does this infection spread to other sites. Bacteremia is also a frequent complication of infection with other gram-negative organisms, including Haemophilus influenzae. In some cases, air may fill up the area between the pleural membranes causing the lungs to collapse, a condition called pneumothorax. It can be a complication of pneumonia (particularly Streptococcus pneumoniae) or of some of the invasive procedures used to treat pleural effusion. In rare cases, infection may spread from the lungs to the heart and can even spread throughout the body, sometimes causing abscesses in the brain and other organs. Severe hemoptysis (coughing up blood) is another potentially serious complication of pneumonia, particularly in patients with other lung problems such as cystic fibrosis.