Having cystic fibrosis would it be unsafe to travel to a third world country?

Depends. If a child has minimal symptoms from his cf, he might be fine. He will have more trouble getting medical care in a third world country if he becomes ill, however. The more complicated the CF is, the more risky such a trip would be.
A big "it depends" Well, there is third world and there is "third world". Obviously with CF there is a big risk of becoming colonized with new bacteria, and that exposure is much greater there than here. That said, if your pulmonologist is cool with it, it's probably ok. A lot depends on your degree of lung function, how long you're going to stay there, and how much contact there will be. Tb is a big risk.
Avoid smoke exposure. Exposure to infections and smoke ( from cigarettes or open fires used to cook ) may worsen CF lung disease. Many CF patients travel with appropriate precautions, vaccines and avoiding situations that may lead to a CF complication. Taking your CF medications, nebulizer and adhering to your medical regimen and chest pt will help you have a good trip.

Related Questions

If your child has cystic fibrosis would it definitely show up on the heel prick test?

No. Most mutations that cause CF are known and are tested for at birth. However, rare subtypes (that are generally not as severe) are not all typed yet and therefor aren't tested for. Read more...
CF screening. The test performed at birth is a screening test and may miss some cases of cf. If your child develops symptoms of the disease or if there is a family history of cf, a follow up test may be ordered by your physician. Read more...