It may be time to call the Center for Disease Control, because an outbreak of major proportions is immanent in the Seattle area. My fair city could very well be the next Hot Zone, but there is still time to prevent catastrophe if they act soon.
If the CDC takes this seriously, they will call in the military for support, have them swoop down on Seattle and the surrounding area immediately, set up an impenetrable quarantine zone, and hope for everyones sake that this thing hasn't gone airborne.
All roads will need to be blocked. All ships held in port. All flights grounded without delay. Dare I say anyone attempting to leave the area will have to be dealt with using the harshest of measures.
Then, once an impenetrable barrier has been established, they would be wise to call in someone with experience. Somebody who has been on the front lines of a major outbreak in the past (I'm thinking Dustin Hoffman or Will Smith, maybe both) hand them giant square-headed orange haz mat suits with extra long hoses attached to the back, and send them walking methodically in the direction of the LIAYF household while making those loud, air suctiony sounds.
As they approach, The Fresh Prince and The Rain Man, or whomever is ultimately sent will, depending on the progression of the outbreak, undoubtedly have to maneuver around the scattered bodies laying limp and motionless, many with both hands clutching their midsections, the effects of the outbreak having run its course with them.
Then, once inside the LIAYF home they will need to be prepared to use whatever means to find and stifle Patient Zero. I would suggest serious faces, stern looks, or deep breaths targeted directly at the subject. If those don't work, they may have to employ extreme measures - An offer a diversionary treat, or more effectively a story, preferrably from a book with colorful pictures!
But again I stress, it's time to act now. Without haste. I'm sounding this warning because I have seen it first hand before and know how quickly it can spread.
This 4-year-olds laughter is highly contagious.
Honest. They must act now or people won't know what hit them.