Assumptions of WHO guidelines:
(1) transmission is rare if flights are less than 8 hours
(2) air filtration on a plane is working as specified
(3) passengers are usually in their seats
Risk factors for a person exposed:
(1) immunosuppression
(2) frequent flier or flight attendant
Risk factors associated with the airplane
(1) defect in air handling (not running, poor filtration, etc)
Risk factors associated with the source person:
(1) untreated cavitary tuberculosis
(2) frequent, repetitive flights (commuting by air; air attendant) or a flight > 8 hours
(3) mobile within the plane
(4) more virulent strain
Risk factors associated with a population:
(1) high prevalence of untreated tuberculosis in the people flying on the airline
