Overview of pneumonia
Pneumonia is an infection of the lungs. It can be caused by bacteria, viruses or fungi. Antibiotics have reduced the fatalities associated from pneumonia many fold. Prior to the discovery of antibiotics, about one-third of people who developed pneumonia died from the infection. There has been a steep decline in the number of deaths due to pneumonia since 1940, when penicillin became widely available. In the later years, the decline was increasing annually probably due to the increased coverage of medical services across the population. There was a rise in the number of deaths in 1957 due to the influenza A pandemic.1 In 2000, the number of patients in a homecare setting with admission in the hospital with a primary diagnosis of pneumonia in USA was 20,300 (1.5%).2 In a 2004 survey, pneumonia and influenza together were the 8th leading cause of death in the USA .3
Route of transmission of pneumonia
Pneumonia is frequently categorized by cough, sneezing, runny nose and other upper respiratory symptoms. The infection is transmitted from person to person through a sneeze or a cough when small droplets containing the pathogens are discharged into the air. Inhalation of these fine droplets with the pathogens by any person results in the person getting infected. Apart from this mode of transmission, pneumonia can be caused by the entry of bacteria or viruses that are normally present in the mouth, throat or nose inadvertently into the lung. It happens in some conditions like during sleep, when some people aspirate secretions from the mouth, throat or nose, during vomiting when there is severe continuous vomiting and the person gasps for air sucking the vomitus into the lungs. Normally, the body has a very good reflex response where secretions are generally not allowed to enter the lungs. As soon as any foreign particle enters the lung space, the cough reflex is initiated to discharge that particle. Also, the 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, children and people in their old age, immunocompromised people are more prone to get pneumonia than the general population. The organisms enter the lungs and multiply rapidly. Depending on the organism and the area of infiltration, it can develop into lobar or segmental pneumonia.
Classification of pneumonia
Pneumonia can be classified as
- community-acquired pneumonia or
- hospital-acquired pneumonia (nosocomial).
As the name suggests, community-acquired pneumonia is acquired by any person outside the hospital setting. Sometimes, a person can get admitted to the hospital due to some other illness or for some surgery and get infected in the hospital. A hospital is a place where a number of patients arrive and depart for consultation, investigation, treatment or follow-up. Despite stringent methods to make sure that patients come and get treated and go without leaving any pathogens or microorganism behind, some organisms manage to survive all the aseptic precautions and thrive in the hospital setting. These cause pneumonia in a previously healthy individual who has come to the hospital for some other purpose. This infection is known as nosocomial pneumonia. It is defined as any pneumonia developing in an individual 72 hafter being in a hospital. Among these two, nosocomial pneumonia is the most serious because of the simple reason that for an organism to survive in a hospital setting with all the aseptic techniques, the organism will usually have developed good resistance to most antibiotics and therefore will pose a significant challenge for treatment.
The organisms responsible for causing pneumonia can be divided as follows:
- Typical: Organisms causing typical pneumonia are the Streptococcus pneumoniae, Staphylococcus and Haemophilus
- Atypical. Organisms known to cause the atypical pneumonia are the Mycoplasma, Legionella and Chlamydia
Streptococcus pneumoniae is the most common cause of bacterial pneumonia. It is usually of abrupt onset and accompanied by chills, fever, and production of a rust-colored sputum. A vaccine (Pneumovax) is available against S. pneumoniae and is recommended for infants, elderly and people with diabetes, chronic heart, lung or kidney disease. This is usually well-managed with the use of antibiotics. Antibiotics commonly used in the treatment of this pneumonia include penicillin, amoxicillin and clavulanic acid (Augmentin and Augmentin XR), macrolide antibiotics including erythromycin, azithromycin (Zithromax and Zmax), and clarithromycin (Biaxin).
Haemophilus influenza is another bacterium that causes pneumonia in the susceptible persons. For treating this infection, antibiotics that can be used are amoxicillin and clavulanic acid, second- and third-generation cephalosporins, fluoroquinolones (levofloxacin [Levaquin]), moxifloxacin-oral (Avelox), gatifloxacin-oral (Tequin), and sulfamethoxazole and trimethoprim (Bactrim and Septra).
Mycoplasma pneumoniae is one of the atypical pneumonias. Symptoms include fever, chills, muscle aches, diarrhea and rash. This bacterium is the principal cause of many pneumonias in the summer and fall months. Macrolides (erythromycin, clarithromycin, azithromycin and fluoroquinolones) are antibiotics commonly prescribed to treat Mycoplasma pneumoniae.
Legionnaire’s disease is caused by the bacterium Legionella pneumoniae and is most often found in contaminated water supplies and air conditioners. It is a potentially fatal infection if not accurately diagnosed. Pneumonia is just a 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 condition.
The other major cause of pneumonias is virus. 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.
Apart from bacterial and viral sources that can cause pneumonia, fungal infections that can lead to pneumonia include actinomycosis, cryptococcosis, aspergillosis, histoplasmosis, coccidiomycosis, blastomycosis and nocardiosis. These are responsible for a relatively small percentage of pneumonias in USA. Each fungus has specific antifungal and antibiotic treatments, which are amphotericin B, fluconazole (Diflucan), penicillin and sulfonamides.
Overuse of antibiotics has become a major concern in the medical community. Most sore throats and upper respiratory infections are caused by viruses rather than bacteria. The rationale for prescribing antibiotics in a viral condition is to avoid any secondary bacterial infection and in suspected bacterial condition. But lately, there has been prescription of antibiotics in all cases of sore throats and upper respiratory infections. 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, vs. hospital-acquired pneumonia).
Although resistant organisms were usually found in nosocomial or hospital-acquired infections, recently, one of these resistant organisms from the hospital has become quite common in the community. In some communities, up to 50% of S. aureus infections are due to organisms resistant to the antibiotic methicillin. This organism is referred to as MRSA (methicillin-resistant S. aureas) and requires special antibiotics when it causes infection. It is frequently known to cause skin infections but can cause pneumonia too.
Signs and symptoms of pneumonia
The signs and symptoms of pneumonia are basically of the upper respiratory infection. Most people initially have symptoms of a cold followed by a high fever (sometimes as high as 104ºF), shaking chills, and a cough with sputum production. The sputum is usually discolored and sometimes bloody. Patients may have breathing difficulties and shortness of breath. Chest pain may develop if the outer aspects of the lung are involved. This pain is known as pleuritic pain and is usually sharp and worsens when taking a deep breath. 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.
While the above symptoms may be present in most of the population, in some populations the symptoms may not be very obvious. 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. Caution has to be exercised in diagnosing and treating these patients because delays can prove fatal.
Diagnosis of pneumonia
In most cases, pneumonia may be suspected clinically 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.
To confirm the diagnosis and the organism, sputum samples can be collected and examined under the microscope. To further confirm the finding of a microorganism, a sample of the sputum can be grown in special incubators, and the offending bacteria 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 is done to assess the severity of the infection. A 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.
Bronchoscopy is a procedure in which a bronchoscope (thin, flexible, tube with fibreoptics to view the structures at the front of the tube) is inserted into the nose or mouth after a local anesthetic is administered to eliminate or reduce the pain. The breathing passages can then be directly examined by the doctor, and specimens from the infected part of the lung can be obtained.
Legionella urinary antigen test is done if there is clinical suspicion of Legionnaire’s disease.
Treatment options of pneumonia
Guidelines for the treatment of diseases are published by the related societies in the respective nations. These are based on prior evidence of clinical benefit from specific therapies. The evidence is graded to provide a clear understanding.
- Level I—High level of evidence. Evidence from well-conducted, randomized controlled trials.
- Level II—Moderate level of evidence. Evidence from well-designed, controlled trials without randomization. (Randomization is a process where research participants are assigned to either the investigational group or the control group randomly (by chance not by choice). The goal of randomization is to produce comparable groups in terms of general participant characteristics, such as age or gender, and other key factors that affect the probable course the disease would take. A randomized, controlled trial is considered the most reliable and impartial method of determining what medical interventions work the best).
- Level III – Low level of evidence. Evidence from case studies and expert opinion. In some instances, therapy recommendations come from antibiotic susceptibility data without clinical observations.
In USA, two of the most widely referenced guidelines for the treatment of CAP are those of the Infectious Diseases Society of America (IDSA) and the American Thoracic Society (ATS).4 In response to confusion regarding differences between their respective guidelines, the IDSA and the ATS convened a joint committee to develop a unified CAP guideline document. The guidelines can be adapted to suit local regulations and practices.
- Previously healthy and no use of antimicrobials within the previous 3 months
- A macrolide (strong recommendation; level I evidence)
- Doxycyline (weak recommendation; level III evidence)
- Presence of comorbidities such as chronic heart, lung, liver or renal disease; diabetes mellitus; alcoholism; malignancies; asplenia; immunosuppressing conditions or use of immunosuppressing drugs; or use of antimicrobials within the previous 3 months (in which case an alternative from a different class should be selected)
- A respiratory fluoroquinolone (moxifloxacin, gemifloxacin, or levofloxacin [750 mg]) (strong recommendation; level I evidence)
- A β-lactam plus a macrolide (strong recommendation; level I evidence)
- In regions with a high rate (125%) of infection with high-level macrolide-resistant Streptococcus pneumoniae, consider the use of alternative agents listed above in (2) for patients without comorbidities (moderate recommendation; level III evidence).
Inpatients and Non-ICU Treatment
- A respiratory fluoroquinolone (strong recommendation; level I evidence)
- A β-lactam plus a macrolide (strong recommendation; level I evidence)
- Inpatients, ICU treatment
A β-lactam (cefotaxime, ceftriaxone, or ampicillin-sulbactam) plus either azithromycin (level II evidence) or a respiratory fluoroquinolone (level I evidence) (strong recommendation) (for penicillin-allergic patients, a respiratory fluoroquinolone and aztreonam are recommended)
If community acquired-methicillin resistant Staphylococcus aureus (CA-MRSA) is a consideration, add vancomycin or linezolid (moderate recommendation; level III evidence).
Pneumonia is a serious illness that requires a visit to the doctor to assess it’s severity and start therapy. If diagnosed and treated at the right time, it is a very easily manageable condition. In case of an elderly person or babies or children or immunocompromised people developing upper respiratory signs and symptoms, medical attention becomes necessary to rule out or treat pneumonia.
- Dowell SF, Kupronis BA, Zell ER, Shay DK. Mortality from pneumonia in children in the United States, 1939 through 1996, N Engl J Med. 2000; 342: 1399–1407.
- The National Home and Hospice Care Survey, United States, 2000.
- National Vital Statistics Reports, Vol. 55, No. 19, August 21, 2007.
- Mandell LA,, Wunderink RG, Anzueto A, Bartlett JG, Campbell GD, Dean NC, et al. Infectious Diseases Society of America/American Thoracic Society Consensus Guidelines on the Management of Community-Acquired Pneumonia in Adults, Clinical Infectious Diseases 2007; 44: S27–72.