What are some of the organisms that cause pneumonia? What is the treatment for pneumonia? Can pneumonia be prevented?
Two vaccines are available to prevent pneumococcal disease: the pneumococcal conjugate vaccine (PCV13) 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. This vaccination should be repeated every five to seven years, whereas the flu vaccine is given annually.
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 (E-Mycin, Eryc, Ery-Tab, PCE, Pediazole, Ilosone), azithromycin (Zithromax, Z-Max), 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], and sulfamethoxazole/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 (see above) 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. In the past, this condition was referred to as "walking pneumonia," a term that is rarely used today. These infections are very difficult to distinguish clinically and often require laboratory evidence for confirmation.
Recently, a study performed in the Netherlands demonstrated that adding a steroid medication, dexamethasone (Decadron), to antibiotic therapy shortens the duration of hospitalization. This medication should be used with caution in patients whom are critically ill or already have a compromised immune system.
Pneumocystis carinii (now known as Pneumocystis jiroveci) 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. More recently, H1N1, swine-origin influenza A, has been associated with very severe pneumonia often resulting in respiratory failure. This disease often requires the use of mechanical ventilation for breathing support. Death is not uncommon when this infection involves the lungs.
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. The situation with MRSA continues to evolve. The community-acquired strain of MRSA tends to be responsive to some of the more commonly used antibiotics whereas the hospital-acquired strains require stronger, more aggressive antibiotic therapies. As this evolution occurs, patients are arriving in the hospital with the community-acquired strains as well as a previous hospital-acquired strain. This further necessitates performing bacterial cultures to determine the best course of action.
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