Pneumonia overview

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Priyamvada Singh, M.D. [2]

Overview

Pneumonia is an illness of the lungs and respiratory system in which the alveoli (microscopic air-filled sacs of the lung responsible for absorbing oxygen from the atmosphere) become inflamed and flooded with fluid. Pneumonia can result from a variety of causes, including infection with bacteria, viruses, fungi, parasites, and chemical or physical injury to the lungs. Typical symptoms associated with pneumonia include cough, chest pain, fever, and difficulty in breathing. Diagnostic tools include x-rays and an examination of the sputum. Treatment depends on the cause of pneumonia; bacterial pneumonia is treated with antibiotics. Pneumonia is a common illness which occurs in all age groups, and is a leading cause of death among the elderly and people who are chronically and terminally ill. Vaccines to prevent certain types of pneumonia are available. The prognosis depends on the type of pneumonia, the appropriate treatment, any complications, and the person's underlying health.

American Thoracic Society (ATS) and the Infectious Disease Society of America (IDSA) Definitions of Hospital Acquired Pneumonia, Ventilator-Associated Pneumonia, and Health Care Associated Pneumonia (DO NOT EDIT)

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Hospital-Acquired Pneumonia (HAP) HAP is defined as pneumonia that occurs 48 hours or more after admission, which was not incubating at the time of admission Ventilator-Associated Pneumonia (VAP) VAP refers to pneumonia that arises more than 48–72 hours after endotracheal intubation. Some patients may require intubation after developing severe HAP and should be managed similar to patients with VAP. Healthcare-Associated Pneumonia (HCAP) HCAP includes any patient who was hospitalized in an acute care hospital for two or more days within 90 days of the infection; resided in a nursing home or long-term care facility; received recent intravenous antibiotic therapy, chemotherapy, or wound care within the past 30 days of the current infection; or attended a hospital or hemodialysis clinic.

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Classification

Aspiration Pneumonia

Aspiration pneumonia (or aspiration pneumonitis) is caused by aspirating foreign objects which are usually oral or gastric contents. This can occur either while eating or after reflux or vomiting which results in bronchopneumonia. The resulting lung inflammation is not an infection but can contribute to one, since the material aspirated may contain anaerobic bacteria or other unusual causes of pneumonia. Aspiration is a leading cause of death among hospital and nursing home patients, since they often cannot adequately protect their airways and may have otherwise impaired defenses.

Parasitic Pneumonia

A variety of parasites can affect the lungs. It is a rare cause of pneumonia, occurring almost exclusively in immunocompromised persons, such as persons suffering from AIDS. This is a respiratory infection that may or may not be serious. There are a variety of parasites which can affect the lungs. In general, these parasites enter the body through the skin or by being swallowed. Once inside the body, these parasites travel to the lungs, most often through the blood. There, a similar combination of cellular destruction and immune responses cause a disruption of oxygen transportation. One type of white blood cell, the eosinophil, responds vigorously to parasite infection. Eosinophils in the lungs can lead to eosinophilic pneumonia, thus complicating the underlying parasitic pneumonia. The most common parasites involved are toxoplasma gondii, strongyloides stercoralis, ascariasis, and hookworm.

Eosinophilic Pneumonia

Eosinophilic pneumonia (EP) is a disease in which a certain type of white blood cell called an eosinophil accumulates in the lung. These cells cause disruption of the normal air spaces (alveoli) where oxygen is extracted from the atmosphere. Several different kinds of eosinophilic pneumonia exist and can occur in any age group. The most common symptoms include cough, fever, difficulty breathing, and sweating at night. EP is diagnosed by a combination of characteristic symptoms, findings on a physical examination by a health provider, and the results of blood tests and x-rays. Prognosis is excellent once EP is recognized and treatment with corticosteroids is begun.

Pathophysiology

Bacteria and fungi typically enter the lung with inhalation. Once inside the alveoli, these microbes travel into the spaces between the cells and also between adjacent alveoli through connecting pores. This invasion triggers the immune system response by sending white blood cells responsible for attacking microorganisms (neutrophils) to the lungs resulting in manifestations of pneumonia.

Causes

Pneumonia can be caused by viral, bacterial, and fungal organisms. The etiology depends upon various factors like age, immune status, geographical area, and comorbid conditions.

Epidemiology and Demographics

Pneumonia is a common illness in all parts of the world. It is a major cause of death among all age groups. Mortality from pneumonia generally decreases with age until late adulthood. Elderly individuals, however, are at particular risk for pneumonia and associated mortality. More cases of pneumonia occur during the winter months than during other times of the year. Pneumonia occurs more commonly in males than females, and more often in African Americans than caucasians. Individuals with underlying illnesses such as Alzheimer's disease, cystic fibrosis, emphysema, tobacco smoking, alcoholism, or immune system problems are at increased risk for pneumonia. These individuals are also more likely to have repeated episodes of pneumonia. People who are hospitalized for any reason are also at high risk for pneumonia. Following urinary tract infections, this is the second most common cause of nosocomial infections, and its prevalence is 15-20% of the total number

Risk Factors

The risk factors for pneumonia include: smoking, age, immuno-suppression, exposure to chemicals, underlying lung disease, and exposure to chemicals.

Diagnosis

Diagnostic Criteria

Community acquired pneumonia should be distinguished from healthcare-associated pneumonia as these diseases have different causative organism, prognosis, diagnostic and treatment guidelines.

History and Symptoms

People with pneumonia often have a productive cough, fever, shaking chills, shortness of breath, pleuritic chest pain,hemoptysis, headaches, diaphoresis, and clammy skin. Other possible symptoms are loss of appetite, fatigue,blueness of the skin, nausea, vomiting, mood swings, andjoint pains or muscle aches. In elderly people manifestations of pneumonia may not be typical. They may develop a new or worsening confusion or may experience unsteadiness, leading to falls. Infants with pneumonia may have many of the symptoms above, but in many cases they are simply sleepy or have a decreased appetite.

Physical Examination

Physical examination may reveal fever or sometimes low body temperature, an increased respiratory rate, low blood pressure, a fast heart rate, or a low oxygen saturation, which is the amount of oxygen in the blood as indicated by either pulse oximetry or blood gas analysis. Patients who are struggling to breathe, who are confused, or who have cyanosis (blue-tinged skin) require immediate attention. Auscultation findings include lack of normal breath sounds, the presence of crackling sounds (rales), or increased loudness of whispered speech (whispered pectoriloquy) with areas of the lung that are stiff and full of fluid, called consolidation. Vital signs are useful in determining the severity of illness and have predictive values. However, a high degree of suspicion should be kept in elderly as the presentation could be subtle in them.

Laboratory Findings

Laboratory findings such as leukocytosis are helpful for the diagnosis of bacterial pneumonia or to assess the status of the patient. Sputum samples need to be collected from every patient and gram staining and culture need to be performed to determine the exact pathogen causing the pneumonia. Other tests include urine antigen test, PCR, C-reactive protein and procalcitonin.

Chest X Ray

An important test for making a diagnosis of pneumonia is a chest x-ray. Chest x-rays can reveal areas of opacity (seen as white) which represent consolidation. Pneumonia is not always seen on x-rays, either because the disease is only in its initial stages, or because it involves a part of the lung not easily seen by x-ray.

CT

A chest CT scan is not routinely done in patients with pneumonia, but is a diagnostic test that may be useful when a chest X-ray is not conclusive. CT findings may include lobar consolidation, ground-glass oppacities, pleural effusion, lymphadenopathy, and tree-in-bud appereance.

Treatment

Medical Therapy

The treatment of pneumonia involves three critical decisions: firstly whether the patient truly has pneumonia, secondly what is the severity of the pneumonia, and lastly whether hospitalization is required for adequate management. Most cases of pneumonia can be treated without hospitalization. Typically, oral antibiotics, rest, fluids, and home care are sufficient for complete resolution. However, people with pneumonia who are having trouble breathing, comorbidities, and the elderly may need more advanced treatment. If the symptoms get worse, the pneumonia does not improve with home treatment, or complications occur, the person will often have to be hospitalized.

Prevention

There are several ways to prevent infectious pneumonia. Appropriately treating underlying illnesses (such as AIDS), smoking cessation, vaccination against pneumococcal, and influenza are the commonly used methods.