Update - MRSA is GONE ! Bye-Bye!
Confusion is often created by sputum tests. They in fact, can't show what you haven't got, they can only show what you have. A negative test is not proof that the organism is gone, it just proves that the sputum is fresh, or comes from a healthy part of the lung which is not colonized. I've had PA since 1992 and as I'm fit and generally unproductive I regularly produce PA free sputum samples, but I still have it. I've also known people with B.cepacia to be declared free of it, to have it pop up in 6 months with exactly the same pattern of sensitivities.
Staph infections don't keep PA away. PA can't live in a normal healthy lung. Staph comes along and repeated infections cause sufficient lung damage to make the PWCF vulnerable to PA. Therefore people with staph infections tend to be younger and fitter. Older people like myself (42) are more likely to culture PA. However early identification and prompt treatment in early PA infections can irradicate it.
This obviously does not mean that the MRSA has not gone, and I hope it has. Make sure your daughter takes all the antibiotics and she stands a good chance of getting rid of the PA. I went seven years between the first time I grew PA and the time I became permanently infected in 1992. And until a bout of TB earlier this year my FEV1 remained above 100% (currently 80% and rising).
I hope this information is not too disturbing. I find knowledge is power in CF and if you understand the science of bacteria it puts you in a very good position to fight it. Good luck.