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.

Although some disagreement exists on the exact boundary between the upper and lower respiratory tracts, the upper respiratory tract is generally considered to be the airway above the glottis or vocal cords. This includes the nose, sinuses, pharynx, and larynx.

Typical infections of the upper respiratory tract include tonsillitis, pharyngitis, laryngitis, sinusitis, otitis media, certain types of influenza, and the common cold. Symptoms of URIs can include cough, sore throat, runny nose, nasal congestion, headache, low grade fever, facial pressure and sneezing.

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.

Respiratory tract infection (RTI) refers to any of a number of infectious diseases involving the respiratory tract. An infection of this type is normally further classified as an upper respiratory tract infection (URI or URTI) or a lower respiratory tract infection (LRI or LRTI). Lower respiratory infections, such as pneumonia, tend to be far more serious conditions than upper respiratory infections, such as the common cold.

"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.

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.

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.

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.

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

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.

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.

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.

Infectious diseases causing ILI include malaria, acute HIV/AIDS infection, herpes, hepatitis C, Lyme disease, rabies, myocarditis, Q fever, dengue fever, poliomyelitis, pneumonia, measles, and many others.

Pharmaceutical drugs that may cause ILI include many biologics such as interferons and monoclonal antibodies. Chemotherapeutic agents also commonly cause flu-like symptoms. Other drugs associated with a flu-like syndrome include bisphosphonates, caspofungin, and levamisole. A flu-like syndrome can also be caused by an influenza vaccine or other vaccines, and by opioid withdrawal in addicts.

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.

Initial symptoms are flu-like and may include fever, myalgia, lethargy symptoms, cough, sore throat, and other nonspecific symptoms. The only symptom common to all patients appears to be a fever above . SARS may eventually lead to shortness of breath and/or pneumonia; either direct viral pneumonia or first bacterial pneumonia.

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.

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.

Influenza-like illness (ILI), also known as acute respiratory infection (ARI) and flu-like syndrome/symptoms, is a medical diagnosis of "possible" influenza or other illness causing a set of common symptoms.

Symptoms commonly include fever, shivering, chills, malaise, dry cough, loss of appetite, body aches, and nausea, typically in connection with a sudden onset of illness. In most cases, the symptoms are caused by cytokines released by immune system activation, and are thus relatively non-specific.

Common causes of ILI include the common cold and influenza, which tends to be less common but more severe than the common cold. Less-common causes include side effects of many drugs and manifestations of many other diseases.

Acute bronchitis, also known as a chest cold, is short term inflammation of the bronchi of the lungs. The most common symptom is a cough. Other symptoms include coughing up mucus, wheezing, shortness of breath, fever, and chest discomfort. The infection may last from a few to ten days. The cough may persist for several weeks afterwards with the total duration of symptoms usually around three weeks. Some have symptoms for up to six weeks.

Bronchitis may be indicated by an expectorating cough, shortness of breath (dyspnea), and wheezing. On occasion, chest pains, fever, and fatigue or malaise may also occur. In addition, bronchitis caused by Adenoviridae may cause systemic and gastrointestinal symptoms as well. However, the coughs due to bronchitis can continue for up to three weeks or more even after all other symptoms have subsided.

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.

Those infected with the virus may be asymptomatic or develop flu-like symptoms such as fever, cough, fatigue, and shortness of breath. Emergency symptoms include difficulty breathing, persistent chest pain or pressure, confusion, difficulty waking, and bluish face or lips; immediate medical attention is advised if these symptoms are present. Less commonly, upper respiratory symptoms such as sneezing, runny nose or sore throat may be seen. Gastrointestinal symptoms such as nausea, vomiting and diarrhoea have been observed in varying percentages. Some cases in China initially presented only with chest tightness and palpitations. In some, the disease may progress to pneumonia, multi-organ failure, and death. In those who develop severe symptoms, time from symptom onset to needing mechanical ventilation is typically eight days.

Loss of smell was identified as a common early symptom of COVID-19 in March 2020, although not as common as initially reported.

As is common with infections, there is a delay between the moment when a person is infected with the virus and the time when they develop symptoms. This is called the incubation period. The incubation period for COVID-19 is typically five to six days but may range from two to 14 days. 97.5% of people who develop symptoms will do so within 11.5 days of infection.

Reports indicate that not all who are infected develop symptoms. The role of these asymptomatic carriers in transmission is not yet fully known; however, preliminary evidence suggests that they may contribute to the spread of the disease. The proportion of infected people who do not display symptoms is currently unknown and being studied, with the Korea Centers for Disease Control and Prevention (KCDC) reporting that 20% of all confirmed cases remained asymptomatic during their hospital stay. China's National Health Commission began including asymptomatic cases in its daily cases on 1 April; of the 166 infections on that day, 130 (78%) were asymptomatic at the time of testing.

Chronic bronchitis is defined as a productive cough that lasts for three months or more per year for at least two years. Most people with chronic bronchitis have chronic obstructive pulmonary disease (COPD). Protracted bacterial bronchitis is defined as a chronic productive cough with a positive bronchoalveolar lavage that resolves with antibiotics. Symptoms of chronic bronchitis may include wheezing and shortness of breath, especially upon exertion and low oxygen saturations. The cough is often worse soon after awakening and the sputum produced may have a yellow or green color and may be streaked with specks of blood.

SARS may be "suspected" in a patient who has:

- Any of the symptoms, including a fever of or higher, and

- Either a history of:

1. Contact (sexual or casual) with someone with a diagnosis of SARS within the last 10 days OR

2. Travel to any of the regions identified by the World Health Organization (WHO) as areas with recent local transmission of SARS (affected regions as of 10 May 2003 were parts of China, Hong Kong, Singapore and the town of Geraldton, Ontario, Canada).

For a case to be considered "probable," a chest X-ray must be positive for atypical pneumonia or respiratory distress syndrome.

The World Health Organization (WHO) has added the category of "laboratory confirmed SARS" for patients who would otherwise be considered ""probable"" but who have not yet had a positive chest X-ray changes, but have tested positive for SARS based on one of the approved tests (ELISA, immunofluorescence or PCR).

When it comes to the chest X-ray the appearance of SARS is not always uniform but generally appears as an abnormality with patchy infiltrates.