My daughter had her tonsils removed when she was 7 years old. She had had multiple ear infections, ear tubes three times, and her adenoids removed before she finally had her tonsils out. We went with removing them because she had suffered from a systemic strep infection three times (you know it's bad when green stuff comes out the bottom. Yeah.).
Anyway, the Pediatric ENT knew her tonsils were big, but he had no idea just how HUGE they were until he went in and took them out. That wasn't the worse of it, though, and that wasn't the reason why he walked out of the post-exam room to see us looking as white as a ghost. No, the lab took our daughter's tonsils and opened them to do a pathology report, like they always do. Her tonsils were COMPLETELY full of strep. Remind you--she had been given a CLEAN BILL of health before she went into surgery. The strep didn't show up on any of the lab tests! AND, with all the antibiotics the doctors had pumped into her body the first 7 years of her life, the strep had migrated to her tonsils and the antibiotics apparently couldn't/didn't touch it there.
She is now 11 years old and hasn't had strep, a cold, flu, or an ear infection since we had her tonsils removed five years ago. Apparently, her body just couldn't reject the strep virus. Maybe there's someone in your family who is "harboring" the virus and so when it breaks out for him/her, then it runs the gamut through the entire family, since all of you have been weakened, thus making it easier for the virus to "invade" your immune system.
You can counteract this by making sure your body and your immune system is the strongest it can be. Eat organic, do away with fast food, processed, prepackaged food, junk food, and limit sugar (including pop). Give your body high quality supplements like a daily multivitamin, Vit D3 (it's winter; everyone is deficient or low in this at this time of the year), and a multi-mushroom complex (mushrooms are very, very good for the immune system). Start researching and look for any supplement that will confers/help strengthen the immune system.
Our family (me, my husband, our 11 years old) has been taking high quality supplements, eating organic, and drinking reverse-osmosis water for the past four years; we don't get sick anymore.Strengthening the immune system will go a long ways toward warding off any type of cold, virus, or bacteria.