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.

An oral whole cell nontypeable Haemophilus influenzae vaccine may protect against the disease, but "the evidence is mixed".

The diagnosis is typically made by clinical examination. Chest X-ray is sometimes useful to exclude bacterial pneumonia, but not indicated in routine cases.

Testing for the specific viral cause can be done but has little effect on management and thus is not routinely recommended. RSV testing by direct immunofluorescence testing on nasopharyngeal aspirate had a sensitivity of 61% and specificity of 89%. Identification of those who are RSV-positive can help for: disease surveillance, grouping ("cohorting") people together in hospital wards to prevent cross infection, predicting whether the disease course has peaked yet, reducing the need for other diagnostic procedures (by providing confidence that a cause has been identified).

Infants with bronchiolitis between the age of two and three months have a second infection by bacteria (usually a urinary tract infection) less than 6% of the time. Preliminary studies have suggested that elevated procalcitonin levels may assist clinicians in determining the presence of bacterial coinfection, which could prevent unnecessary antibiotic use and costs.

Croup is typically diagnosed based on signs and symptoms. The first step is to exclude other obstructive conditions of the upper airway, especially epiglottitis, an airway foreign body, subglottic stenosis, angioedema, retropharyngeal abscess, and bacterial tracheitis.

A frontal X-ray of the neck is not routinely performed, but if it is done, it may show a characteristic narrowing of the trachea, called the steeple sign, because of the subglottic stenosis, which resembles a steeple in shape. The steeple sign is suggestive of the diagnosis, but is absent in half of cases.

Other investigations (such as blood tests and viral culture) are discouraged, as they may cause unnecessary agitation and thus worsen the stress on the compromised airway. While viral cultures, obtained via nasopharyngeal aspiration, can be used to confirm the exact cause, these are usually restricted to research settings. Bacterial infection should be considered if a person does not improve with standard treatment, at which point further investigations may be indicated.

Antibiotics do not help the many lower respiratory infections which are caused by parasites or viruses. While acute bronchitis often does not require antibiotic therapy, antibiotics can be given to patients with acute exacerbations of chronic bronchitis. The indications for treatment are increased dyspnoea, and an increase in the volume or purulence of the sputum. The treatment of bacterial pneumonia is selected by considering the age of the patient, the severity of the illness and the presence of underlying disease. Amoxicillin and doxycycline are suitable for many of the lower respiratory tract infections seen in general practice.

The most commonly used system for classifying the severity of croup is the Westley score. It is primarily used for research purposes rather than in clinical practice. It is the sum of points assigned for five factors: level of consciousness, cyanosis, stridor, air entry, and retractions. The points given for each factor is listed in the adjacent table, and the final score ranges from 0 to 17.

- A total score of ≤ 2 indicates "mild" croup. The characteristic barking cough and hoarseness may be present, but there is no stridor at rest.

- A total score of 3–5 is classified as "moderate" croup. It presents with easily heard stridor, but with few other signs.

- A total score of 6–11 is "severe" croup. It also presents with obvious stridor, but also features marked chest wall indrawing.

- A total score of ≥ 12 indicates impending respiratory failure. The barking cough and stridor may no longer be prominent at this stage.

85% of children presenting to the emergency department have mild disease; severe croup is rare (<1%).

Vaccination helps prevent bronchopneumonia, mostly against influenza viruses, adenoviruses, measles, rubella, streptococcus pneumoniae, haemophilus influenzae, diphtheria, bacillus anthracis, chickenpox, and bordetella pertussis.

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.

A physical examination will often reveal decreased intensity of breath sounds, wheezing, rhonchi, and prolonged expiration. Most physicians rely on the presence of a persistent dry or wet cough as evidence of bronchitis.

A variety of tests may be performed in patients presenting with cough and shortness of breath:

- A chest X-ray is useful to exclude pneumonia which is more common in those with a fever, fast heart rate, fast respiratory rate, or who are old.

- A sputum sample showing neutrophil granulocytes (inflammatory white blood cells) and culture showing that has pathogenic microorganisms such as "Streptococcus" species.

- A blood test would indicate inflammation (as indicated by a raised white blood cell count and elevated C-reactive protein).

Diagnosis is typically based on a person's signs and symptoms. The color of the sputum does not indicate if the infection is viral or bacterial. Determining the underlying organism is typically not needed. Other causes of similar symptoms include asthma, pneumonia, bronchiolitis, bronchiectasis, and COPD. A chest X-ray may be useful to detect pneumonia.

Another common sign of bronchitis is a cough which lasts ten days to three weeks. If the cough lasts a month or a year it may be chronic bronchitis. In addition to having a cough a fever may be present. Acute bronchitis is normally caused by a viral infection. Typically these infections are rhinovirus, para influenza, or influenza. No specific testing is normally needed to diagnose acute bronchitis.

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.

Pneumonia is typically diagnosed based on a combination of physical signs and a chest X-ray. However, the underlying cause can be difficult to confirm, as there is no definitive test able to distinguish between bacterial and non-bacterial origin.

The World Health Organization has defined pneumonia in children clinically based on either a cough or difficulty breathing and a rapid respiratory rate, chest indrawing, or a decreased level of consciousness. A rapid respiratory rate is defined as greater than 60 breaths per minute in children under 2 months old, greater than 50 breaths per minute in children 2 months to 1 year old, or greater than 40 breaths per minute in children 1 to 5 years old. In children, low oxygen levels and lower chest indrawing are more sensitive than hearing chest crackles with a stethoscope or increased respiratory rate. Grunting and nasal flaring may be other useful signs in children less than five years old.

In general, in adults, investigations are not needed in mild cases. There is a very low risk of pneumonia if all vital signs and auscultation are normal. In persons requiring hospitalization, pulse oximetry, chest radiography and blood tests—including a complete blood count, serum electrolytes, C-reactive protein level, and possibly liver function tests—are recommended. Procalcitonin may help determine the cause and support who should receive antibiotics.

The diagnosis of influenza-like illness can be made based on the signs and symptoms; however, confirmation of an influenza infection requires testing. Thus, treatment is frequently based on the presence of influenza in the community or a rapid influenza test.

Physical examination may sometimes reveal low blood pressure, high heart rate, or low oxygen saturation. The respiratory rate may be faster than normal, and this may occur a day or two before other signs. Examination of the chest may be normal, but it may show decreased chest expansion on the affected side. Harsh breath sounds from the larger airways that are transmitted through the inflamed lung are termed bronchial breathing and are heard on auscultation with a stethoscope. Crackles (rales) may be heard over the affected area during inspiration. Percussion may be dulled over the affected lung, and increased, rather than decreased, vocal resonance distinguishes pneumonia from a pleural effusion.

The Centers for Disease Control describe protocol for treating sinusitis while at the same time discouraging overuse of antibiotics:

- Target likely organisms with first-line drugs: Amoxicillin, Amoxicillin/Clavulanate

- Use shortest effective course: Should see improvement in 2–3 days. Continue treatment for 7 days after symptoms improve or resolve (usually a 10–14 day course).

- Consider imaging studies in recurrent or unclear cases: some sinus involvement is frequent early in the course of uncomplicated viral URI

Treatment comprises symptomatic support usually via analgesics for headache, sore throat and muscle aches. Moderate exercise in sedentary subjects with naturally acquired URTI probably does not alter the overall severity and duration of the illness. No randomized trials have been conducted to ascertain benefits of increasing fluid intake.

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

Prevention is by not smoking and avoiding other lung irritants. Frequent hand washing may also be protective. Treatment of acute bronchitis typically involves rest, paracetamol (acetaminophen), and NSAIDs to help with the fever. Cough medicine has little support for its use and is not recommended in children less than six years of age. There is tentative evidence that salbutamol may be useful in those with wheezing; however, it may result in nervousness and tremors. Antibiotics should generally not be used. An exception is when acute bronchitis is due to pertussis. Tentative evidence supports honey and pelargonium to help with symptoms. Getting plenty of rest and fluids is also often recommended.

The WHO has published several testing protocols for the disease. The standard method of testing is real-time reverse transcription polymerase chain reaction (rRT-PCR). The test is typically done on respiratory samples obtained by a nasopharyngeal swab; however, a nasal swab or sputum sample may also be used. Results are generally available within a few hours to two days. Blood tests can be used, but these require two blood samples taken two weeks apart and the results have little immediate value. Chinese scientists were able to isolate a strain of the coronavirus and publish the genetic sequence so laboratories across the world could independently develop polymerase chain reaction (PCR) tests to detect infection by the virus. As of 4 April 2020, antibody tests (which may detect active infections and whether a person had been infected in the past) were in development, but not yet widely used. The Chinese experience with testing has shown the accuracy is only 60 to 70%. The FDA in the United States approved the first point-of-care test on 21 March 2020 for use at the end of that month.

Diagnostic guidelines released by Zhongnan Hospital of Wuhan University suggested methods for detecting infections based upon clinical features and epidemiological risk. These involved identifying people who had at least two of the following symptoms in addition to a history of travel to Wuhan or contact with other infected people: fever, imaging features of pneumonia, normal or reduced white blood cell count or reduced lymphocyte count.

A study asked hospitalized COVID-19 patients to cough into a sterile container, thus producing a saliva sample, and detected virus in eleven of twelve patients using RT-PCR. This technique has the potential of being quicker than a swab and involving less risk to health care workers (collection at home or in the car).

Along with laboratory testing, chest CT scans may be helpful to diagnose COVID-19 in individuals with a high clinical suspicion of infection but is not recommended for routine screening. Bilateral multilobar ground-glass opacities with a peripheral, asymmetric and posterior distribution are common in early infection. Subpleural dominance, crazy paving (lobular septal thickening with variable alveolar filling), and consolidation may appear as the disease progresses.

The best prevention against viral pneumonia is vaccination against influenza, adenovirus, chickenpox, herpes zoster, measles, and rubella.

Prevention of bronchiolitis relies strongly on measures to reduce the spread of the viruses that cause respiratory infections (that is, handwashing, and avoiding exposure to those symptomatic with respiratory infections). In addition to good hygiene an improved immune system is a great tool for prevention. One way to improve the immune system is to feed the infant with breast milk, especially during the first month of life. Immunizations are available for premature infants who meet certain criteria (some cardiac and respiratory disorders) such as Palivizumab (a monoclonal antibody against RSV). Passive immunization therapy requires monthly injections during winter.

Dogs will typically recover from kennel cough within a few weeks. However, secondary infections could lead to complications that could do more harm than the disease itself. Several opportunistic invaders have been recovered from the respiratory tracts of dogs with kennel cough, including Streptococcus, Pasteurella, Pseudomonas, and various coliforms. These bacteria have the potential to cause pneumonia or sepsis, which drastically increase the severity of the disease. These complications are evident in thoracic radiographic examinations. Findings will be mild in animals affected only by kennel cough, while those with complications may have evidence of segmental atelectasis and other severe side effects.

Few data are available about microscopic lesions and the pathophysiology of COVID-19. The main pathological findings at autopsy are:

- Macroscopy: pleurisy, pericarditis, lung consolidation and pulmonary oedema

- Four types of severity of viral pneumonia can be observed:

- minor pneumonia: minor serous exudation, minor fibrin exudation

- mild pneumonia: pulmonary oedema, pneumocyte hyperplasia, large atypical pneumocytes, interstitial inflammation with lymphocytic infiltration and multinucleated giant cell formation

- severe pneumonia: diffuse alveolar damage (DAD) with diffuse alveolar exudates. DAD is the cause of acute respiratory distress syndrome (ARDS) and severe hypoxemia.

- healing pneumonia: organisation of exudates in alveolar cavities and pulmonary interstitial fibrosis

- plasmocytosis in BAL

- Blood: disseminated intravascular coagulation (DIC); leukoerythroblastic reaction

- Liver: microvesicular steatosis

The distinction between viral upper respiratory tract infections is loosely based on the location of symptoms with the common cold affecting primarily the nose, pharyngitis the throat, and bronchitis the lungs. However, there can be significant overlap and multiple areas can be affected. The common cold is frequently defined as nasal inflammation with varying amount of throat inflammation. Self-diagnosis is frequent. Isolation of the viral agent involved is rarely performed, and it is generally not possible to identify the virus type through symptoms.

In cases of viral pneumonia where influenza A or B are thought to be causative agents, patients who are seen within 48 hours of symptom onset may benefit from treatment with oseltamivir or zanamivir. Respiratory syncytial virus (RSV) has no direct acting treatments, but ribavirin in indicated for severe cases. Herpes simplex virus and varicella-zoster virus infections are usually treated with aciclovir, whilst ganciclovir is used to treat cytomegalovirus. There is no known efficacious treatment for pneumonia caused by SARS coronavirus, MERS coronavirus, adenovirus, hantavirus, or parainfluenza. Care is largely supportive.

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.

Antibiotics are given to treat any bacterial infection present. Cough suppressants are used if the cough is not productive. NSAIDs are often given to reduce fever and upper respiratory inflammation. Prevention is by vaccinating for canine adenovirus, distemper, parainfluenza, and "Bordetella". In kennels, the best prevention is to keep all the cages disinfected. In some cases, such as "doggie daycares" or nontraditional playcare-type boarding environments, it is usually not a cleaning or disinfecting issue, but rather an airborne issue, as the dogs are in contact with each other's saliva and breath. Although most kennels require proof of vaccination, the vaccination is not a fail-safe preventative. Just like human influenza, even after receiving the vaccination, a dog can still contract mutated strains or less severe cases.