The owners of most newly-adopted shelter dogs and cats report their pets are doing "extremely well" in their new homes, despite a high incidence of respiratory illness in the first week post-adoption.

From an in-depth review of the study in Animal Sheltering magazine:

Just a week post-adoption, 71 percent of dog owners and 81 percent of cat owners reported that their animals were adjusting to their new homes “extremely well,” and those numbers rose to 73 percent and 88 percent, respectively, one month after adoption.

According to the study, while more than 50 percent of dogs and cats had signs of illness within one week of adoption, that number dropped to around 10 percent at the one-month mark.

Lord LK, et al. Health and behavior problems in dogs and cats one week and one month after adoption from animal shelters. JAVMA; 2008