Infants get sick a lot. On average, a baby experiences three to six episodes of respiratory tract infection during the first year of life. There is a lot of variation, however, from one household to another. Numerous factors affect the frequency and severity of childhood illnesses, such as attending day care, having older siblings, and a parental history of asthma or smoking.
Recently, another factor was identified. Studies show that children exposed to animals—
Can it be true that our “reward” for cleaner living is that we are more likely to get sick?
Could a young child’s exposure to infectious agents really be a good thing? As we saw in the previous section, exposure to pathogens (and the antigens that mark them) causes our immune system to be more effective at fighting later infections. Our immune system learns and remembers. Without early challenges, we may be depriving it of important “learning” opportunities.
This is an issue almost everyone is interested in, and one with significant public health implications, so it’s worth exploring more. Of course, it would not be ethical to deliberately expose infants to pathogens in a randomized, controlled, double-
In 2012, some researchers reported a study in which they examined the effect of contact with dogs and cats on the frequency of respiratory tract illnesses during the first year of life. Using a “prospective birth cohort study,” they observed 397 children until the age of one year, beginning when their mother was pregnant. They collected information on the children through weekly diaries kept by the parents, including information about any contact with dogs or cats and any respiratory symptoms or infections.
Can you think of some difficulties in conducting a prospective cohort study? Some strengths?
Several features of prospective cohort studies make them a valuable tool for scientific thinking. Defining before the study period begins the groups—
How much healthier are kids living with a dog?
The results were dramatic. Children having dogs at home experienced 31% fewer respiratory infections and 44% fewer ear infections, and received 29% fewer antibiotic prescriptions. (The researchers found that cat ownership, too, provided a protective effect, but it was much weaker than for dog ownership.)
In their study, the researchers noted only the amount of animal exposure and the incidence of respiratory tract infections, so they could not offer a definitive explanation for their findings. They speculated, however, that animal contacts were responsible for strengthening the immune system. Specifically, they proposed that (1) animals bring dirt into the home, (2) the more dirt brought in, the greater the diversity of bacteria in the home, and (3) exposure to greater bacterial diversity has a positive effect on maturation of the child’s immune system.
Does it matter whether the dog is indoors a lot or a little?
In some of the homes with dogs, the dog was only occasionally inside (less than 6 hours per day), while in others, the dog was inside “often” (6–
Should we strive to create the most hygienic environment possible for a baby?
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So, how clean should an infant’s environment be? This is a hugely important question and one that the researchers weren’t sure they could answer yet. Still, their finding adds to a growing body of evidence supporting the hygiene hypothesis and suggesting that there are benefits to an environment in which a developing child’s immune system is challenged.
Babies living in homes with dogs gain protection from respiratory illnesses during the first year of life, perhaps because challenges to the immune system make it more effective at fighting infections later.
What factors can influence how frequently an infant gets sick? How would having a dog in the household potentially prevent a child from getting sick as often?