The result was a "clinically based descriptive definition using correlated symptoms" in six symptom groups: fatigue and sleep problems, pain, neurologic and mood, gastrointestinal, respiratory symptoms, and skin (dermatologic) symptoms.To meet the "Kansas" case definition, a veteran of the 1990–91 Gulf War must have symptoms in at least three of the six symptom domains, which during the survey were scored based on severity ("severity"). Symptom onset must have developed during or after deploying to the 1990–91 Gulf War theatre of operations ("onset") and must have been present in the year before interview ("duration"). Participants were excluded if they had a diagnosis of or were being treated for any of several conditions that might otherwise explain their symptoms ("exclusionary criteria"), including cancer, diabetes, heart disease, chronic infectious disease, lupus, multiple sclerosis, stroke, or any serious psychiatric condition.Applying the Kansas case definition to the original Kansas study cohort resulted in a prevalence of Gulf War illness of 34.2% in Gulf War veterans and 8.3% in nondeployed Gulf War era veterans, or an excess rate of GWI of 26.3% in Gulf War veterans. CDC definition
Also in 1998, a study published by Dr. Keiji Fukuda under the auspices of the U.S. Centers for Disease Control and Prevention (CDC) examined chronic multisymptom illness through a cross-sectional survey of 3,675 ill and healthy U.S. Air Force veterans of the 1990–91 Gulf War, including from a Pennsylvania-based Air National Guard unit and three comparison Air Force units.
They often use some of several laboratory methods for diagnosis of bad breath:

Halimeter: a portable sulfide monitor used to test for levels of sulfur emissions (to be specific, hydrogen sulfide) in the mouth air. When used properly, this device can be very effective at determining levels of certain VSC-producing bacteria. However, it has drawbacks in clinical applications. For example, other common sulfides (such as mercaptan) are not recorded as easily and can be misrepresented in test results. Certain foods such as garlic and onions produce sulfur in the breath for as long as 48 hours and can result in false readings. The Halimeter is also very sensitive to alcohol, so one should avoid drinking alcohol or using alcohol-containing mouthwashes for at least 12 hours prior to being tested. This analog machine loses sensitivity over time and requires periodic recalibration to remain accurate. Gas chromatography: portable machines are being studied. This technology is designed to digitally measure molecular levels of major VSCs in a sample of mouth air (such as hydrogen sulfide, methyl mercaptan, and dimethyl sulfide). It is accurate in measuring the sulfur components of the breath and produces visual results in graph form via computer interface. BANA test: this test is directed to find the salivary levels of an enzyme indicating the presence of certain halitosis-related bacteria.