For sinusitis lasting more than 12 weeks a CT scan is recommended. On a CT scan, acute sinus secretions have a radiodensity of 10 to 25 Hounsfield units (HU), but in a more chronic state they become thickened, with a radiodensity of 30 to 60 HU.

Nasal endoscopy and clinical symptoms are also used to make a positive diagnosis. A tissue sample for histology and cultures can also be collected and tested. Allergic fungal sinusitis (AFS) is often seen in people with asthma and nasal polyps. In rare cases, sinusoscopy may be made.

Nasal endoscopy involves inserting a flexible fiber-optic tube with a light and camera at its tip into the nose to examine the nasal passages and sinuses. This is generally a completely painless (although uncomfortable) procedure which takes between five and ten minutes to complete.

Optical fiber endoscopy can confirm the diagnosis in case of doubt, directly visualizing the inflamed adenoid.

Health care providers distinguish bacterial and viral sinusitis by watchful waiting. If a person has had sinusitis for fewer than 10 days without the symptoms becoming worse, then the infection is presumed to be viral. When symptoms last more than 10 days or get worse in that time, then the infection is considered bacterial sinusitis. Imaging by either X-ray, CT or MRI is generally not recommended unless complications develop. Pain caused by sinusitis is sometimes confused for pain caused by pulpitis (toothache) of the maxillary teeth, and vice versa. Classically, the increased pain when tilting the head forwards separates sinusitis from pulpitis.

Sinus films are helpful in the diagnosis of sphenoid sinusitis. Opacification, sclerosis, and air-fluid levels are typical findings. Contrast-enhanced CT scan may reveal underlying sinusitis, thickening of the superior ophthalmic vein, and irregular filling defects within the cavernous sinus; however, findings may be normal early in the disease course.

A MRI using flow parameters and an MR venogram are more sensitive than a CT scan, and are the imaging studies of choice to diagnose cavernous sinus thrombosis. Findings may include deformity of the internal carotid artery within the cavernous sinus, and an obvious signal hyperintensity within thrombosed vascular sinuses on all pulse sequences.

Cerebral angiography can be performed, but it is invasive and not very sensitive. Orbital venography is difficult to perform, but it is excellent in diagnosing occlusion of the cavernous sinus.

CBC, ESR, blood cultures, and sinus cultures help establish and identify an infectious primary source. Lumbar puncture is necessary to rule out meningitis.

In cases of viral adenoiditis, treatment with analgesics or antipyretics is often sufficient. Bacterial adenoiditis may be treated with antibiotics, such as amoxicillin - clavulanic acid or a cephalosporin. In case of adenoid hypertrophy, adenoidectomy may be performed to remove the adenoid.

It is hard to differentiate a viral and a bacterial cause of a sore throat based on symptoms alone. Thus often a throat swab is done to rule out a bacterial cause.

The modified Centor criteria may be used to determine the management of people with pharyngitis. Based on 5 clinical criteria, it indicates the probability of a streptococcal infection.

One point is given for each of the criteria:

- Absence of a cough

- Swollen and tender cervical lymph nodes

- Temperature >

- Tonsillar exudate or swelling

- Age less than 15 (a point is subtracted if age >44)

The McIsaac criteria adds to the Centor:

- Age less than 15: add one point

- Age greater than 45: subtract one point

The Infectious Disease Society of America however recommends against empirical treatment and considers antibiotics only appropriate following positive testing. Testing is not needed in children under three as both group A strep and rheumatic fever are rare, except if they have a sibling with the disease.

Diagnosis is by a swab of the affected area for laboratory testing. A Gram stain is performed to show Gram-positive cocci in chains. Then, the organism is cultured on blood agar with an added bacitracin antibiotic disk to show beta-hemolytic colonies and sensitivity (zone of inhibition around the disk) for the antibiotic. Culture on agar not containing blood, and then performing the catalase test should show a negative reaction for all streptococci. "S. pyogenes" is CAMP and hippurate tests negative. Serological identification of the organism involves testing for the presence of group-A-specific polysaccharide in the bacterium's cell wall using the Phadebact test.

The rapid pyrrolidonyl arylamidase (PYR) test is used for the presumptive identification of group A beta-hemolytic streptococci. GBS gives a negative finding on this test.

Immediate treatment is very important for someone with orbital cellulitis. Treatment typically involves intravenous (IV) antibiotics in the hospital and frequent observation (every 4–6 hours). Along with this several laboratory tests are run including a complete blood count, differential, and blood culture.

- Antibiotic therapy – Since orbital cellulitis is commonly caused by "Staphylococcus" and "Streptococcus" species both penicillins and cephalosporins are typically the best choices for IV antibiotics. However, due to the increasing rise of MRSA (methicillin-resistant "Staphylococcus aureus") orbital cellulitis can also be treated with Vancomycin, Clindamycin, or Doxycycline. If improvement is noted after 48 hours of IV antibiotics, healthcare professions can then consider switching a patient to oral antibiotics (which must be used for 2–3 weeks).

- Surgical intervention – An abscess can threaten the vision or neurological status of a patient with orbital cellulitis, therefore sometimes surgical intervention is necessary. Surgery typically requires drainage of the sinuses and if a subperiosteal abscess is present in the medial orbit, drainage can be performed endoscopically. Post-operatively, patients must follow up regularly with their surgeon and remain under close observation.

Gargling salt water is often suggested but evidence looking at its usefulness is lacking. Alternative medicines are promoted and used for the treatment of sore throats. However, they are poorly supported by evidence.

Although orbital cellulitis is considered an ophthalmic emergency the prognosis is good if prompt medical treatment is received.

Treatment for fungal sinusitis can include surgical debridement; helps by slowing progression of disease thus allowing time for recovery additionally we see the options below:

- In the case of invasive fungal sinusitis, echinocandins, voriconazole, and amphoterecin (via IV) may be used

- For allergic fungal sinusitis, systemic corticosteroids like prednisolone, methylprednisolone are added for their anti-inflammatory effect, bronchodilators and expectorants help to clear secretions in the sinuses.

Antibiotics are aimed at gram positive bacteria. Medical attention should be sought if symptoms persist beyond 2–3 days.

In terms of diagnosis, the clinical examination gives an idea about fungal sinusitis, as well as:

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.

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.

Absolute eosinophil count, nasal smear, skin and in vitro allergy tests to rule out allergic rhinitis, acoustic rhinometry for measuring nasal patency, smell testing, CT scan in cases of sinus disease and MRI in case of mass lesions.

Due to the importance of disease caused by "S. pneumoniae" several vaccines have been developed to protect against invasive infection. The World Health Organization recommend routine childhood pneumococcal vaccination; it is incorporated into the childhood immunization schedule in a number of countries including the United Kingdom, United States, and South Africa.

Depending on the nature of infection an appropriate sample is collected for laboratory identification. Pneumococci are typically gram-positive cocci seen in pairs or chains. When cultured on blood agar plates with added optochin antibiotic disk they show alpha-hemolytic colonies and a clear zone of inhibition around the disk indicating sensitivity to the antibiotic. Pneumococci are also bile soluble. Just like other streptococci they are catalase-negative. A Quellung test can identify specific capsular polysaccharides.

Pneumococcal antigen (cell wall C polysaccharide) may be detected in various body fluids. Older detection kits, based on latex agglutination, added little value above Gram staining and were occasionally false-positive. Better results are achieved with rapid immunochromatography, which has a sensitivity (identifies the cause) of 70–80% and >90% specificity (when positive identifies the actual cause) in pneumococcal infections. The test was initially validated on urine samples but has been applied successfully to other body fluids. Chest X-rays can also be conducted to confirm inflammation though are not specific to the causative agent.

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.

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.

Nose examination: The mucosa is usually boggy and edematous with clear mucoid secretions. The turbinates are congested and hypertrophic.

Pharynx examination: Mucosal injection and lymphoid hyperplasia involving tonsils, adenoids and base of tongue may be seen.

"S. pyogenes" infections are best prevented through effective hand hygiene. No vaccines are currently available to protect against "S. pyogenes" infection, although research has been conducted into the development of one. Difficulties in developing a vaccine include the wide variety of strains of "S. pyogenes" present in the environment and the large amount of time and number of people that will be needed for appropriate trials for safety and efficacy of the vaccine.

Diagnosis of FVR is usually by clinical signs, especially corneal ulceration. Definitive diagnosis can be done by direct immunofluorescence or virus isolation. However, many healthy cats are subclinical carriers of feline herpes virus, so a positive test for FHV-1 does not necessarily indicate that signs of an upper respiratory tract infection are due to FVR. Early in the course of the disease, histological analysis of cells from the tonsils, nasal tissue, or nictitating membrane (third eyelid) may show inclusion bodies (a collection of viral particles) within the nucleus of infected cells.

Treatment generally consists of surgical drainage, and long-term (6 to 8 weeks) use of antibiotics.