In 1997, the International Rhinosinusitis Advisory Board (IRAB) published the clinical classification of rhinosinusitis in adults. They defined acute rhinosinusitis as a sinusitis with an acute onset of symptoms and a duration of symptoms less than 12 weeks and symptoms that resolve completely.

Recurrent acute rhinosinusitis was defined as being more than one and less than four episodes of acute rhinosinusitis per year, a complete recovery between the attacks, and a symptom-free period ofmore than or equal to eight weeks between the acute attacks in absence of medical treatment.

The diagnosis of acute community-acquired bacterial rhinosinusitis (ACABRS) is judged probable if two major criteria (symptoms), or one major and two or more minor criteria, are present.

The authors, however, recognize that none of these criteria are sensitive and specific for the diagnosis of ACABRS, so that an additional standard was necessary to prove the diagnostic accuracy.

Sinus puncture studies had shown that the symptoms that persist longer than 10 days without improvement are suggestive of bacterial rather than viral rhinosinusitis. Hence, if a patient with a cold or influenza illness does not improve or is worse after 10 days, the authors recommended treatment with antibiotics.

Some symptoms such as fever, facial erythema, and maxillary toothache have high specificity but low sensitivity, and when present, the diagnosis of ACABRS is warranted. They recognized that ACABRS needs to be differentiated from acute nosocomial or hospital-acquired bacterial rhinosinusitis (AHABRS).

Nosocomial sinusitis is most often polymicrobial and is usually caused by those organisms that are most prevalent in that particular institution. AHABRS is often seen in critically ill or immunosuppressed patients.

Chronic rhinosinusitis was defined as a sinusitis with a duration of symptoms more than 12 weeks, which shows persistent inflammatory changes on imaging and lasts for more than or equal to four weeks after starting appropriate medical therapy (with no intervening acute episodes).

The authors also defined the acute exacerbation of chronic rhinosinusitis as a worsening of existing symptoms or appearance of new symptoms and a complete resolution of acute (but not chronic) symptoms between episodes.

The authors presented their definitions and classification of infectious rhinosinusitis with a summary of current views on etiology and management. They admitted that the definitions based on the severity and duration of symptoms were imperfect, the duration of the acute episodes chosen in the various definitions was arbitrary, and the clinical significance of abnormal findings on imaging investigation was debatable.

For the duration in the definition of chronic sinusitis, they followed the FDA recommendation to consider the condition if symptoms persist for more than 12 weeks.

From a clinical perception, the authors admitted that the definition of chronic rhinosinusitis (CRS) is often subjective and is based on symptoms that are vague, nonlocalized, and nonspecific. The relationship between the findings on endoscopic examination, the radiographic appearance and specific symptoms, and the severity is poorly defined.

The authors also realize that there appears to be an ill-defined group between the acute and the chronic conditions, and they suggest that this problem can be overcome by the use of the term ‘‘subacute’’ which spans the interval, but in other respects defies the definition, and it does not represent a histopathologic entity.

The IRAB also proposed another classification based on:

• Microbiological etiology, i.e., probable viral rhinosinusitis (nasal congestion, obstruction, nasal discharge, facial pressures/pain without fever, toothache, facial tenderness, erythema, and swelling),
• Acute bacterial rhinosinusitis (same symptoms as viral rhinosinusitis) but with fever-fever is an exclusion criteria for viral rhinosinusitis or persisting without improvement for more than eight days),
• Recurrent acute rhinosinusitis (incidence of more than four episodes a year),
• Chronic sinusitis (with symptoms lasting longer than 12 weeks),
• and Acute exacerbation of chronic rhinosinusitis (acute worsening of chronic sinusitis symptoms).

Although the IRAB recognizes the occurrence of sinusitis in allergic patients, it still considers every sinusitis to be of infectious origin.Their definition requires the inclusion of the parameter of duration in the classification based on the microbiological etiology.

What was not taken into consideration by IRAB is the report by Gwaltney et al. that in maxillary sinus aspirates of patients with acute community acquired sinusitis (ACAS: the most typical example of bacterial sinusitis), viruses and fungi are found in addition to bacteria.

The same working definitions that took into account the duration of the diseases were developed by TFR, sponsored by the American Academy of Otolaryngology/Head and Neck Surgery (AAO-HNS).

This report details the major and minor symptoms and defines sinusitis as the condition manifested by an inflammatory response of the nasal cavity and sinuses, and not an infection of these structures. It prefers the term rhinosinusitis to sinusitis as the mucous blanket of the sinuses is in continuity with that of the nasal cavity.

They recognized that the multifactorial nature and multiple causes of rhinosinusitis make it difficult to define its cause in a given patient. They therefore concluded that it is currently impractical to define rhinosinusitis on the basis of its cause.

An important differentiation between acute and chronic was made on the basis of histopathology, where acute rhinosinusitis is predominantly viewed as an exudative process associated with necrosis, hemorrhage, and/or ulceration, in which neutrophils predominate, whereas CRS is predominantly a proliferative process associated with fibrosis of the lamina propria, in which lymphocytes, plasma cells, and eosinophils predominate along with perhaps changes in bone.

Another important statement by the TRF is that a pathological review may also reveal a variety of findings that include, but are limited to, varying degrees of eosinophils in tissues and secretions, as well as the polyp formation and the presence of granulomas, bacteria, or fungi.

This statement is important as it highlights the importance of inflammation (eosinophilic infiltration) rather than the infection, the presence of fungi, or the formation of nasal polyps in CRS.

The TFR also recognizes the concept of subacute rhinosinusitis for several reasons:

1. When polled, the physicians serving on the TFR indicated that they would treat rhinosinusitis lasting less than two to three weeks differently than they would treat a rhinosinusitis lasting 6 to 12 weeks.

2. Similar issues concerning otitis media had been heatedly debated until the otitis media literature arbitrarily defined acute otitis media as those lasting three weeks, subacute as lasting 3 to 12 weeks, and chronic otitis media as those lasting more than 12 weeks.

3. The FDA had no formal definition to describe the condition that lasts 4 to 12 weeks (less than four weeks is acute, more than four weeks is chronic).

The TFR defines five different classifications of adult rhinosinusitis:

1. Acute rhinosinusitis is a sinusitis with a sudden onset and lasting up to four weeks. The symptoms resolve completely, and once the disease has been treated, antibiotics are no longer required.

A strong history consistent with acute rhinosinusitis includes two or more major factors or one major and two minor factors. However, the finding of nasal purulence is a strong indicator of an accurate diagnosis.

A suggestive history for which acute rhinosinusitis should be included in the differential diagnosis includes one major factor, or two or more minor factors.

In absence of other nasal factors, fever or pain alone does not constitute a strong history. Severe, prolonged, or worsening infections may be associated with a nonviral element.

Factors suggesting acute bacterial sinusitis are the worsening of the symptoms after five days, the persistence of symptoms for more than 10 days, or the presence of symptoms out of proportion to those typically associated with viral URTI.

2. Subacute rhinosinusitis represents a continuum of the natural progression of acute rhinosinusitis that has not resolved. This condition is diagnosed after a four-week duration of acute rhinosinusitis, and it lasts up to 12 weeks.

Patients with subacute rhinosinusitis may or may not have been treated for the acute phase, and the symptoms are less severe than those found in acute rhinosinusitis. Thus, unlike in acute rhinosinusitis, fever would not be considered as amajor factor.

The clinical factors required for the diagnosis of subacute adult rhinosinusitis are the same as for those CRS. Subacute rhinosinusitis usually resolves completely after an effective medical regimen.

3. Recurrent acute rhinosinusitis is defined by symptoms and physical findings consistent with acute rhinosinusitis, with these symptoms and findings worsening after five days or when persisting more than 10 days.

However, each episode lasts 7 to 10 days or more, and may last up to four weeks. Furthermore, four or more than four episodes occur in one year.

Between episodes, symptoms are absent without concurrent medical therapy. The diagnostic criteria for recurrent acute rhinosinusitis are otherwise identical to those of acute rhinosinusitis.

4. Chronic rhinosinusitis is rhinosinusitis lasting more than 12 weeks. The diagnosis is confirmed by the major and minor clinical factor complex with or without findings on the physical examination.

A strong history consistent with chronic rhinosinusitis includes the presence of two or more major factors, or one major and two minor factors.

A history suggesting that CRS should be considered in the differential diagnosis includes two or more minor factors or one major factor. Facial pain does not contribute a strong history in the absence of other nasal factors.

5. Acute exacerbation of chronic rhinosinusitis represents sudden worsening of the baseline CRS with either worsening or new symptoms. Typically the acute (non-chronic) symptoms resolve completely between occurrences.