Symptoms of viral pneumonia include fever, non-productive cough, runny nose, and systemic symptoms (e.g. myalgia, headache). Different viruses cause different symptoms.

Viral pneumonia is a pneumonia caused by a virus.

Viruses are one of the two major causes of pneumonia, the other being bacteria; less common causes are fungi and parasites. Viruses are the most common cause of pneumonia in children, while in adults bacteria are a more common cause.

The incubation period is 5–7 days (with a range of 3–10). Symptoms can include a harsh, dry cough, retching, sneezing, snorting, gagging or vomiting in response to light pressing of the trachea or after excitement or exercise. The presence of a fever varies from case to case.

Usually the atypical causes also involve atypical symptoms:

- No response to common antibiotics such as sulfonamide and beta-lactams like penicillin.

- No signs and symptoms of lobar consolidation, meaning that the infection is restricted to small areas, rather than involving a whole lobe. As the disease progresses, however, the look can tend to lobar pneumonia.

- Absence of leukocytosis.

- Extrapulmonary symptoms, related to the causing organism.

- Moderate amount of sputum, or no sputum at all (i.e. non-productive).

- Lack of alveolar exudate.

- Despite general symptoms and problems with the upper respiratory tract (such as high fever, headache, a dry irritating cough followed later by a productive cough with radiographs showing consolidation), there are in general few physical signs. The patient looks better than the symptoms suggest.

"Pharyngoconjunctival fever" is a specific presentation of adenovirus infection, manifested as:

- high fever that lasts 4–5 days

- pharyngitis (sore throat)

- conjunctivitis (inflamed eyes, usually without pus formation like pink eye)

- enlargement of the lymph nodes of the neck

- headache, malaise, and weakness

- Incubation period of 5–9 days

It usually occurs in the age group 5–18. It is often found in summer camps and during the spring and fall in schools. In Japan, the illness is commonly referred to as "pool fever" as it is often spread via public swimming pools.

Lower respiratory tract infection (LRTI), while often used as a synonym for pneumonia, can also be applied to other types of infection including lung abscess and acute bronchitis. Symptoms include shortness of breath, weakness, fever, coughing and fatigue.

There are a number of symptoms that are characteristic of lower respiratory tract infections. The two most common are bronchitis and edema. Influenza affects both the upper and lower respiratory tracts.

Antibiotics are the first line treatment for pneumonia; however, they are not effective or indicated for parasitic or viral infections. Acute bronchitis typically resolves on its own with time.

In 2015 there were about 291 million cases. These resulted in 2.74 million deaths down from 3.4 million deaths in 1990. This was 4.8% of all deaths in 2013.

Bronchitis describes the swelling or inflammation of the bronchial tubes. Additionally, bronchitis is described as either acute or chronic depending on its presentation and is also further described by the causative agent. Acute bronchitis can be defined as acute bacterial or viral infection of the larger airways in healthy patients with no history of recurrent disease. It affects over 40 adults per 1000 each year and consists of transient inflammation of the major bronchi and trachea. Most often it is caused by viral infection and hence antibiotic therapy is not indicated in immunocompetent individuals. Viral bronchitis can sometimes be treated using antiviral medications depending on the virus causing the infection, and medications such as anti-inflammatory drugs and expectorants can help mitigate the symptoms. Treatment of acute bronchitis with antibiotics is common but controversial as their use has only moderate benefit weighted against potential side effects (nausea and vomiting), increased resistance, and cost of treatment in a self-limiting condition. Beta2 agonists are sometimes used to relieve the cough associated with acute bronchitis. In a recent systematic review it was found there was no evidence to support their use.

Apart from respiratory involvement, illnesses and presentations of adenovirus include gastroenteritis, conjunctivitis, cystitis, and rash illness. Symptoms of respiratory illness caused by adenovirus infection range from the common cold syndrome to pneumonia, croup, and bronchitis. Patients with compromised immune systems are especially susceptible to severe complications of adenovirus infection. Acute respiratory disease (ARD), first recognized among military recruits during World War II, can be caused by adenovirus infections during conditions of crowding and stress.

People with infectious pneumonia often have a productive cough, fever accompanied by shaking chills, shortness of breath, sharp or stabbing chest pain during deep breaths, and an increased rate of breathing. In the elderly, confusion may be the most prominent sign.

The typical signs and symptoms in children under five are fever, cough, and fast or difficult breathing. Fever is not very specific, as it occurs in many other common illnesses, may be absent in those with severe disease, malnutrition or in the elderly. In addition, a cough is frequently absent in children less than 2 months old. More severe signs and symptoms in children may include blue-tinged skin, unwillingness to drink, convulsions, ongoing vomiting, extremes of temperature, or a decreased level of consciousness.

Bacterial and viral cases of pneumonia usually present with similar symptoms. Some causes are associated with classic, but non-specific, clinical characteristics. Pneumonia caused by "Legionella" may occur with abdominal pain, diarrhea, or confusion, while pneumonia caused by "Streptococcus pneumoniae" is associated with rusty colored sputum, and pneumonia caused by "Klebsiella" may have bloody sputum often described as "currant jelly". Bloody sputum (known as hemoptysis) may also occur with tuberculosis, Gram-negative pneumonia, and lung abscesses as well as more commonly with acute bronchitis. "Mycoplasma" pneumonia may occur in association with swelling of the lymph nodes in the neck, joint pain, or a middle ear infection. Viral pneumonia presents more commonly with wheezing than does bacterial pneumonia. Pneumonia was historically divided into "typical" and "atypical" based on the belief that the presentation predicted the underlying cause. However, evidence has not supported this distinction, thus it is no longer emphasized.

Croup is characterized by a "barking" cough, stridor, hoarseness, and difficulty breathing which usually worsens at night. The "barking" cough is often described as resembling the call of a seal or sea lion. The stridor is worsened by agitation or crying, and if it can be heard at rest, it may indicate critical narrowing of the airways. As croup worsens, stridor may decrease considerably.

Other symptoms include fever, coryza (symptoms typical of the common cold), and indrawing of the chest wall–known as Hoover's sign. Drooling or a very sick appearance indicate other medical conditions, such as epiglottitis.

In a typical case, an infant under two years of age develops cough, wheeze, and shortness of breath over one or two days. Crackles or wheeze are typical findings on listening to the chest with a stethoscope. The infant may be breathless for several days. After the acute illness, it is common for the airways to remain sensitive for several weeks, leading to recurrent cough and wheeze.

Some signs of severe disease include:

- poor feeding (less than half of usual fluid intake in preceding 24 hours)

- significantly decreased activity

- history of stopping breathing

- respiratory rate >70/min

- presence of nasal flaring and/or grunting

- severe chest wall recession (Hoover's sign)

- bluish skin

Kennel cough (also known as canine infectious tracheobronchitis) is an upper respiratory infection affecting dogs. There are multiple causative agents, the most common being the bacterium "Bordetella bronchiseptica" (found in 78.7% of cases in Southern Germany), followed by canine parainfluenza virus (37.7% of cases), and to a lesser extent canine coronavirus (9.8% of cases). It is highly contagious; however adult dogs may display immunity to reinfection even under constant exposure. Kennel cough is so named because the infection can spread quickly among dogs in the close quarters of a kennel or animal shelter.

Viral and bacterial causes of canine cough are spread through airborne droplets produced by sneezing and coughing. These agents also spread through contact with contaminated surfaces. Symptoms begin after a several day incubation period post-exposure, and in most cases will clear up on their own. However, in young puppies or immunocompromised animals, mixed or secondary infections can progress to lower respiratory infections such as pneumonia.

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.

Chest radiographs (X-ray photographs) often show a pulmonary infection before physical signs of atypical pneumonia are observable at all.

This is occult pneumonia. In general, occult pneumonia is rather often present in patients with pneumonia and can also be caused by "Streptococcus pneumoniae", as the decrease of occult pneumonia after vaccination of children with a pneumococcal vaccine suggests.

Infiltration commonly begins in the perihilar region (where the bronchus begins) and spreads in a wedge- or fan-shaped fashion toward the periphery of the lung field. The process most often involves the lower lobe, but may affect any lobe or combination of lobes.

Croup is usually deemed to be due to a viral infection. Others use the term more broadly, to include acute laryngotracheitis, spasmodic croup, laryngeal diphtheria, bacterial tracheitis, laryngotracheobronchitis, and laryngotracheobronchopneumonitis. The first two conditions involve a viral infection and are generally milder with respect to symptomatology; the last four are due to bacterial infection and are usually of greater severity.

Pneumonitis refers to lung inflammation; pneumonia refers to pneumonitis, usually due to infection but sometimes non-infectious, that has the additional feature of pulmonary consolidation. Pneumonia is most commonly classified by where or how it was acquired: community-acquired, aspiration, healthcare-associated, hospital-acquired, and ventilator-associated pneumonia. It may also be classified by the area of lung affected: lobar pneumonia, bronchial pneumonia and acute interstitial pneumonia; or by the causative organism. Pneumonia in children may additionally be classified based on signs and symptoms as non-severe, severe, or very severe.

The setting in which pneumonia develops is important to treatment, as it correlates to which pathogens are likely suspects, which mechanisms are likely, which antibiotics are likely to work or fail, and which complications can be expected based on the person's health status.

Bronchiolitis is blockage of the small airway in the lungs due to a viral infection. It usually only occurs in children less than two years of age. Symptoms may include fever, cough, runny nose, wheezing, and breathing problems. More severe cases may be associated with nasal flaring, grunting, or the skin between the ribs pulling in with breathing. If the child has not been able to feed properly, signs of dehydration may be present.

Bronchiolitis is usually the result of infection by respiratory syncytial virus (72% of cases) or human rhinovirus (26% of cases). Diagnosis is generally based on symptoms. Tests such as a chest X-ray or viral testing are not routinely needed. Urine testing may be considered in those with a fever.

There is no specific treatment. Supportive care at home is generally sufficient. Occasionally hospital admission for oxygen, support with feeding, or intravenous fluids is required. Evidence for antibiotics, antivirals, bronchodilators, or nebulized hypertonic saline or epinephrine is either unclear or not supportive.

About 10% to 30% of children under the age of two years are affected by bronchiolitis at some point in time. It more commonly occurs in the winter in the Northern hemisphere. The risk of death among those who are admitted to hospital is about 1%. Outbreaks of the condition were first described in the 1940s.

Signs and symptoms of PCP include fever, non-productive cough (because sputum is too viscous to become productive), shortness of breath (especially on exertion), weight loss, and night sweats. There is usually not a large amount of sputum with PCP unless the patient has an additional bacterial infection. The fungus can invade other visceral organs (such as the liver, spleen, and kidney), but only in a minority of cases.

Pneumothorax is a well-known complication of PCP. An acute history of chest pain with breathlessness and diminished breath sounds is typical of pneumothorax.

New or progressive infiltrate on the chest X-ray with one of the following:

- Fever > 37.8 °C (100 °F)

- Purulent sputum

- Leukocytosis > 10,000 cells/μl

In an elderly person, the first sign of hospital-acquired pneumonia may be mental changes or confusion.

Other symptoms may include:

- A cough with greenish or pus-like phlegm (sputum)

- Fever and chills

- General discomfort, uneasiness, or ill feeling (malaise)

- Loss of appetite

- Nausea and vomiting

- Sharp chest pain that gets worse with deep breathing or coughing

- Shortness of breath

- Decreased blood pressure and fast heart rate

"Streptococcus pneumoniae" () is the most common bacterial cause of pneumonia in all age groups except newborn infants. "Streptococcus pneumoniae" is a Gram-positive bacterium that often lives in the throat of people who do not have pneumonia.

Other important Gram-positive causes of pneumonia are "Staphylococcus aureus" () and "Bacillus anthracis".

Pneumonia is an illness which can result from a variety of causes, including infection with bacteria, viruses, fungi, or parasites. Pneumonia can occur in any animal with lungs, including mammals, birds, and reptiles.

Symptoms associated with pneumonia include fever, fast or difficult breathing, nasal discharge, and decreased activity.

Different animal species have distinct lung anatomy and physiology and are thus

affected by pneumonia differently. Differences in anatomy, immune systems, diet, and behavior also affects the particular microorganisms commonly causing

pneumonia. Diagnostic tools include physical examination, testing of the

sputum, and x-ray investigation. Treatment depends on the cause of pneumonia;

bacterial pneumonia is treated with antibiotics.

"See also:" Pneumonia, Pneumonic.

Over 100 microorganisms can cause CAP, with most cases caused by "Streptococcus pneumoniae". Certain groups of people are more susceptible to CAP-causing pathogens; for example, infants, adults with chronic conditions (such as chronic obstructive pulmonary disease), senior citizens, alcoholics and others with compromised immune systems are more likely to develop CAP from "Haemophilus influenzae" or "Pneumocystis carinii". A definitive cause is identified in only half the cases.

Some patients have an underlying problem which increases their risk of infection. Some risk factors are:

- "Obstruction": When part of the airway (bronchus) leading to the alveoli is obstructed, the lung cannot eliminate fluid; this can lead to pneumonia. One cause of obstruction, especially in young children, is inhalation of a foreign object such as a marble or toy. The object lodges in a small airway, and pneumonia develops in the obstructed area of the lung. Another cause of obstruction is lung cancer, which can block the flow of air.

- "Lung disease": Patients with underlying lung disease are more likely to develop pneumonia. Diseases such as emphysema and habits such as smoking result in more-frequent and more-severe bouts of pneumonia. In children, recurrent pneumonia may indicate cystic fibrosis or pulmonary sequestration.

- "Immune problems": Immune-deficient patients, such as those with HIV/AIDS, are more likely to develop pneumonia. Other immune problems range from severe childhood immune deficiencies, such as Wiskott–Aldrich syndrome, to the less-severe common variable immunodeficiency.

Bacterial pneumonia is a type of pneumonia caused by bacterial infection.

"M. pneumoniae" infections can be differentiated from other types of pneumonia by the relatively slow progression of symptoms. A positive blood test for cold-hemagglutinins in 50–70% of patients after 10 days of infection (cold-hemagglutinin-test should be used with caution or not at all, since 50% of the tests are false-positive), lack of bacteria in a Gram-stained sputum sample, and a lack of growth on blood agar.

PCR has also been used.

Hospital-acquired pneumonia (HAP) or nosocomial pneumonia refers to any pneumonia contracted by a patient in a hospital at least 48–72 hours after being admitted. It is thus distinguished from community-acquired pneumonia. It is usually caused by a bacterial infection, rather than a virus.

HAP is the second most common nosocomial infection (after urinary tract infections) and accounts for 15–20% of the total. It is the most common cause of death among nosocomial infections and is the primary cause of death in intensive care units.

HAP typically lengthens a hospital stay by 1–2 weeks.