Influenza (ENARM)

Pneumonia is the infection of the lung parenchyma, resulting from the spread of pathogens and accompanied by the host inflammatory response. This condition is the most common infectious cause of death. Multiple organisms cause pneumonia, including bacteria (of which Streptococcus pneumoniae is the most common), viruses, and fungi. The infection can be acquired while hospitalized (hospital-acquired) or outside the hospital setting (community-acquired). Common symptoms include fever, chills, cough, chest pain, and dyspnea. Chest X-ray usually shows consolidation and/or infiltrates. Diagnosis can be made with clinical presentation and imaging, but in severe cases, microbiological testing (sputum and cultures, molecular testing) and routine blood tests are needed. Empiric treatment with antibiotics is recommended, with regimen depending on the setting, risk factors for multidrug-resistant organisms, and individual comorbidities. Identification of the causative pathogen helps narrow down the antibiotics. Preventive measures include vaccinations (pneumococcal and influenza) and smoking cessation.

Diagnostic modalities such as chest X-rays provide static images of the thoracic cavity, including the lungs and airways. While providing a wealth of anatomical information necessary for the diagnosis of pulmonary disease, chest X-rays do not give much information about the individual's respiratory function. Pulmonary function tests are a group of diagnostic procedures yielding useful, quantifiable information about the rate of the flow of air through the individual's airways, lung capacity, and the efficiency of gas exchange in relation to time. The most commonly utilized tests include spirometry (before and after bronchodilator use), lung volumes, and quantitation of diffusing capacity for carbon monoxide (CO). The tests can be influenced by the individual's effort/fatigue, disease state, or anatomical malformation.

Antiviral agents against influenza are important in preventing and treating influenza infection. Influenza is often self-limited, but high-risk populations suffer significant morbidity and mortality from the illness. Different classes of drugs act on the influenza virus. Neuraminidase inhibitors include oseltamivir (oral), zanamivir (inhalation) and peramivir (IV); these drugs act by inhibiting neuraminidase, the enzyme that cleaves off the new virus particle. By blocking the enzymatic effect, further release of progeny virus to nearby respiratory cells is reduced. Baloxavir, a selective inhibitor of influenza cap-dependent endonuclease, inhibits viral mRNA synthesis. Both neuraminidase inhibitors and baloxavir have activity against influenzas A and B. Adamantanes, or M2 inhibitors, include amantadine and rimantadine, which are active against influenza A but are not often used owing to resistance.

Influenza viruses are members of the Orthomyxoviridae family and the causative organisms of influenza, a highly contagious febrile respiratory disease. There are 3 primary influenza viruses (A, B, and C) and various subtypes, which are classified based on their virulent surface antigens, hemagglutinin (HA) and neuraminidase (NA). Influenza typically presents with a fever, myalgia, headache, and symptoms of an upper respiratory infection. Symptoms of gastroenteritis may also commonly occur in children. Influenza is usually a self-limiting condition, though viral or secondary bacterial pneumonia may complicate the disease. Management is generally supportive, although NA inhibitors can be helpful if initiated within 48 hours of infection. Prevention relies on the annual vaccination of the public and practicing good hygiene.

Vaccination is the administration of a substance to induce the immune system to develop protection against a disease. Unlike passive immunization, which involves the administration of pre-performed antibodies, active immunization constitutes the administration of a vaccine to stimulate the body to produce its own antibodies. A vaccine is usually an antigenic, non-virulent form of a normally virulent microorganism. Vaccinations are a form of primary prevention and are the most effective form due to their safety, efficacy, low cost, and easy access. While the majority of vaccines are administered to young patients, some vaccines are targeted to diseases that occur in middle and old age, and are therefore administered to older patients.

Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy.