Pneumonia occurs in a variety of situations and treatment must vary according to the situation. It is classified as either community or hospital acquired depending on where the patient contracted the infection. It is life-threatening in the elderly or those who are immunocompromised. The most common treatment is antibiotics and these vary in their adverse effects and their effectiveness. Pneumonia is also the leading cause of death in children less than five years of age in low income countries. The most common cause of pneumonia is pneumococcal bacteria, "Streptococcus pneumoniae" accounts for 2/3 of bacteremic pneumonias. This is a dangerous type of lung infection with a mortality rate of around 25%.

For optimal management of a pneumonia patient, the following must be assessed: pneumonia severity (including treatment location, e.g., home, hospital or intensive care), identification of causative organism, analgesia of chest pain, the need for supplemental oxygen, physiotherapy, hydration, bronchodilators and possible complications of emphysema or lung abscess.

Bronchiolitis typically affects infants and children younger than two years, principally during the fall and winter . Bronchiolitis hospitalization has a peak incidence between two and six months of age and remains a significant cause of respiratory disease during the first two years of life. It is a leading cause of hospitalization in infants and young children.

Lower respiratory tract infections place a considerable strain on the health budget and are generally more serious than upper respiratory infections.

Normal surgical masks and N95 masks appear equivalent with respect to preventing respiratory infections.

A 2014 systematic review of clinical trials does not support using routine rapid viral testing to decrease antibiotic use for children in emergency departments. It is unclear if rapid viral testing in the emergency department for children with acute febrile respiratory infections reduces the rates of antibiotic use, blood testing, or urine testing. The relative risk reduction of chest x-ray utilization in children screened with rapid viral testing is 77% compared with controls. In 2013 researchers developed a breath tester that can promptly diagnose lung infections.

Several studies found that healthcare-associated pneumonia is the second most common type of pneumonia, occurring less commonly than community-acquired pneumonia but more frequently than hospital-acquired pneumonia and ventilator-associated pneumonia. In a recent observational study, the rates for CAP, HCAP and HAP were 60%, 25% and 15% respectively. Patients with HCAP are older and more commonly have simultaneous health problems (such as previous stroke, heart failure and diabetes).

The number of residents in long term care facilities is expected to rise dramatically over the next 30 years. These older adults are known to develop pneumonia 10 times more than their community-dwelling peers, and hospital admittance rates are 30 times higher.

The term usually refers to acute viral bronchiolitis, a common disease in infancy. This is most commonly caused by respiratory syncytial virus (RSV, also known as human pneumovirus). Other viruses which may cause this illness include metapneumovirus, influenza, parainfluenza, coronavirus, adenovirus, and rhinovirus.

Children born prematurely (less than 35 weeks), with a low birth weight or who have from congenital heart disease may have higher rates of bronchiolitis and are more likely to require hospital admission. There is evidence that breastfeeding provides some protection against bronchiolitis.

Among the factors contributing to contracting HAP are mechanical ventilation (ventilator-associated pneumonia), old age, decreased filtration of inspired air, intrinsic respiratory, neurologic, or other disease states that result in respiratory tract obstruction, trauma, (abdominal) surgery, medications, diminished lung volumes, or decreased clearance of secretions may diminish the defenses of the lung. Also, poor hand-washing and inadequate disinfection of respiratory devices cause cross-infection and are important factors.

When comparing the bacterial-caused atypical pneumonias with these caused by real viruses (excluding bacteria that were wrongly considered as viruses), the term "atypical pneumonia" almost always implies a bacterial cause and is contrasted with viral pneumonia.

Known viral causes of atypical pneumonia include respiratory syncytial virus (RSV), influenza A and B, parainfluenza, adenovirus, severe acute respiratory syndrome (SARS)

and measles.

Mycoplasma is found more often in younger than in older people.

Older people are more often infected by Legionella.

There is low or very-low quality evidence that probiotics may be better than placebo in preventing acute URTIs. Vaccination against influenza viruses, adenoviruses, measles, rubella, "Streptococcus pneumoniae", "Haemophilus influenzae", diphtheria, "Bacillus anthracis", and "Bordetella pertussis" may prevent them from infecting the URT or reduce the severity of the infection.

Children have 2-9 viral respiratory illnesses per year. In 2013 18.8 billion cases of upper respiratory infections were reported. As of 2014, upper respiratory infections caused about 3,000 deaths down from 4,000 in 1990. In the United States, URIs are the most common infectious illness in the general population. URIs are the leading reasons for people missing work and school.

Respiratory disease is a common and significant cause of illness and death around the world. In the US, approximately 1 billion "common colds" occur each year. A study found that in 2010, there were approximately 6.8 million emergency department visits for respiratory disorders in the U.S. for patients under the age of 18. In 2012, respiratory conditions were the most frequent reasons for hospital stays among children.

In the UK, approximately 1 in 7 individuals are affected by some form of chronic lung disease, most commonly chronic obstructive pulmonary disease, which includes asthma, chronic bronchitis and emphysema.

Respiratory diseases (including lung cancer) are responsible for over 10% of hospitalizations and over 16% of deaths in Canada.

In 2011, respiratory disease with ventilator support accounted for 93.3% of ICU utilization in the United States.

Adenovirus can cause severe necrotizing pneumonia in which all or part of a lung has increased translucency radiographically, which is called Swyer-James Syndrome. Severe adenovirus pneumonia also may result in bronchiolitis obliterans, a subacute inflammatory process in which the small airways are replaced by scar tissue, resulting in a reduction in lung volume and lung compliance.

In Belgium the prevalence of nosocomial infections is about 6.2%. Annually about 125,500 patients become infected by a nosocomial infection, resulting in almost 3000 deaths. The extra costs for the health insurance are estimated to be approximately €400 million/year.

Estimates ranged from 6.7% in 1990 to 7.4% (patients may have several infections). At national level, prevalence among patients in health care facilities was 6.7% in 1996, 5.9% in 2001 and 5.0% in 2006. The rates for nosocomial infections were 7.6% in 1996, 6.4% in 2001 and 5.4% in 2006.

In 2006, the most common infection sites were urinary tract infections (30,3%), pneumopathy (14,7%), infections of surgery site (14,2%). Infections of the skin and mucous membrane (10,2%), other respiratory infections (6,8%) and bacterial infections / blood poisoning (6,4%). The rates among adult patients in intensive care were 13,5% in 2004, 14,6% in 2005, 14,1% in 2006 and 14.4% in 2007.

Nosocomial infections are estimated to make patients stay in the hospital four to five additional days. Around 2004-2005, about 9,000 people died each year with a nosocomial infection, of which about 4,200 would have survived without this infection.

Pulmonary diseases may also impact newborns, such as pulmonary hyperplasia, pulmonary interstitial emphysema (usually preterm births), and infant respiratory distress syndrome,

Post-viral cough can be resistant to treatment. Post-viral cough usually goes away on its own; however, cough suppressants containing codeine may be prescribed. A study has claimed theobromine in dark chocolate is more effective.

One possible cause for post-viral cough is that the receptors that are responsible for stimulating the cough during the respiratory tract infection are up-regulated by respiratory tract infection and continue to stimulate even after the virus has disappeared.

While antibiotics with activity specifically against "M. pneumoniae" are often used (e.g., erythromycin, doxycycline), it is unclear if these result in greater benefit than using antibiotics without specific activity against this organism in those with an infection acquired in the community.

"Mycoplasma pneumoniae" is spread through respiratory droplet transmission. Once attached to the mucosa of a host organism, "M. pneumoniae" extracts nutrients, grows, and reproduces by binary fission. Attachment sites include the upper and lower respiratory tract, causing pharyngitis, bronchitis, and pneumonia. The infection caused by this bacterium is called atypical pneumonia because of its protracted course and lack of sputum production and wealth of extrapulmonary symptoms. Chronic "Mycoplasma" infections have been implicated in the pathogenesis of rheumatoid arthritis and other rheumatological diseases.

"Mycoplasma" atypical pneumonia can be complicated by Stevens–Johnson syndrome, autoimmune hemolytic anemia, cardiovascular diseases, encephalitis, or Guillain–Barré syndrome.

Bacterial tracheitis is a bacterial infection of the trachea and is capable of producing airway obstruction.

One of the most common causes is "Staphylococcus aureus" and often follows a recent viral upper respiratory infection. Bacterial tracheitis is a rare complication of influenza infection. It is the most serious in young children, possibly because of the relatively small size of the trachea that gets easily blocked by swelling. The most frequent sign is the rapid development of stridor. It is occasionally confused with croup.

If it is inflamed, a condition known as tracheitis can occur. In this condition there can be inflammation of the linings of the trachea. A condition called tracheo-bronchitis can be caused, when the mucous membrane of the trachea and bronchi swell. A collapsed trachea is formed as a result of defect in the cartilage, that makes the cartilage unable to support the trachea and results in dry hacking cough. In this condition there can be inflammation of the linings of the trachea. If the connective nerve tissues in the trachea degenerate it causes tracheomalacia. Infections to the trachea can cause tracheomegaly.

In more severe cases, it is treated by administering intravenous antibiotics and may require admission to an intensive care unit (ICU) for intubation and supportive ventilation if the airway swelling is severe. During an intensive care admission, various methods of invasive and non-invasive monitoring may be required, which may include ECG monitoring, oxygen saturation, capnography and arterial blood pressure monitoring.

Safe and effective adenovirus vaccines were developed for adenovirus serotypes 4 and 7, but were available only for preventing ARD among US military recruits, and production stopped in 1996. Strict attention to good infection-control practices is effective for stopping transmission in hospitals of adenovirus-associated disease, such as epidemic keratoconjunctivitis. Maintaining adequate levels of chlorination is necessary for preventing swimming pool-associated outbreaks of adenovirus conjunctivitis.

Most household disinfectants will inactivate FHV-1. The virus can survive up to 18 hours in a damp environment, but less in a dry environment and only shortly as an aerosol.