Dogs protect against childhood infection claim

“Why a dog is a child’s best friend: They bring immune-boosting dirt and allergens into the home,” is today’s headline in the Daily Mail.

So is this proof that your pooch can protect your children from illness or more of a shaggy dog story?

The quick answer is that the evidence, while compelling, is certainly not conclusive.

The news is based on the results of a study that followed babies during their first year of life. It found that children who had contact with a dog had fewer respiratory tract infections (any infection of the sinuses, throat, airways or lungs).

One possible reason to explain the results of the study is that close contact with a family pet could expose babies to germs and allergens (allergy causing substances such as dander) at an early age. It is thought that early exposure to germs and allergens may boost a child’s immune system so they develop a resistance to infections. However, this research did not investigate how dogs may be having a protective effect or whether it is the dirt and allergens found on dogs that results in the reduction in respiratory infections.

It is also important to stress that a family dog should never be left unsupervised with young children; whatever its previous history of behaviour.

Where did the story come from?

The study was carried out by researchers from Kuopio University Hospital; the National Institute for Health and Welfare and the University of Eastern Finland, all in Finland, as well as the University of Ulm in Germany.

The study was funded by grants from the Foundation for Pediatric Research, the Kerttu and Kalle Viikki, Päivikki, the Sakari Sohlberg and the Juho Vainio Foundations’ EVO funding, Farmers’ Social Insurance Institution-Mela; the Academy of Finland, Kupio University Hospital, all in Finland, and the European Union.

The study was published in the peer-reviewed journal Pediatrics.

This story was covered in the Daily Mail. The headline of the story in the paper suggested that a mechanism for the association between dog contact and health had been found. However, the scientific paper only reported the association and suggested possible explanations – these were not tested or proven.

What kind of research was this?

This was a prospective cohort study. It aimed to describe the effect of dog and cat exposure on respiratory tract infections during the first year of a child’s life.

A prospective cohort study, where the data is collected as the study progresses, is the ideal study design to answer this question, although this study design cannot show a causative relationship. This is because there could be other reasons (called confounders) for any observed relationship.

A randomised controlled trial would be required to show causation but it is unlikely that this would be performed to answer this question.

What did the research involve?

The researchers collected data on 397 children born in suburban and rural Finland from pregnancy until one year of age. Every week, diary questionnaires were completed, monitoring the health of the child. If the child had not been completely healthy, parents were asked whether the child had a cough, wheezing, rhinitis (causing sneezing and a blocked, itchy and runny nose), fever, middle ear infection, diarrhoea, urinary tract infection, itchy rash or some other illness during the last seven days.

The diary questionnaires also monitored how much dog or cat contact had taken place during the week, and whether the child had been breastfed.

In addition, the researchers collected data on the whole year at the end of the study using a one-year questionnaire, which again asked mothers to estimate the average amount of daily cat and dog contact.

Information was also collected on where the child lived (on a farm, in the countryside or in the suburbs), when the child was born, their birthweight, the number of older siblings, whether the mother smoked, whether the parents had asthma, allergic eczema or rhinitis, and parental education.

The researchers then looked at whether there was an association between animal contacts and overall healthiness, fever and antibiotic usage, taking into account factors that could be responsible for the interaction seen, including:

• the child’s gender
• the living environment (farm, rural non-farming or suburban)
• the number of siblings
• maternal smoking
• whether the parents had asthma, allergic eczema or rhinitis
• whether the child was breastfed
• birthweight
• season of birth
• diary month

What were the basic results?

The researchers found that children who had dogs at home:

• were healthier/had fewer respiratory tract symptoms or infections (adjusted odds ratio [OR]1.31; 95% confidence interval [CI] 1.13 to 1.52)
• had fewer ear infections (adjusted OR 0.56; 95% CI 0.38 to 0.81)
• required fewer courses of antibiotics (adjusted OR 0.71; 95% CI 0.52 to 0.96)

The highest protective association was seen in children who had a dog inside at home for less than six hours daily or had a dog temporarily or often inside. The researchers suggest that this is because these dogs could bring in the largest amount of dirt, positively impacting on the development of the child’s immune system, although this hypothesis was not tested in the study.

The associations seen did not change if families who avoided pet contact because of allergy were excluded.

How did the researchers interpret the results?

The researchers conclude that their results ‘suggest that dog contacts may have a protective effect on respiratory tract infections during the first year of life’. They say their findings, ‘support the theory that during the first year of life, animal contacts are important, possibly leading to better resistance to infectious respiratory illnesses during childhood’.

Conclusion

This well-designed study found that contact with a dog may have a protective effect against respiratory tract infections during the first year of life. However, there are several limitations to this study, including:

• That this was a prospective cohort study and therefore only an association could be found. Causation cannot be shown as the researchers cannot exclude the possibility that there is another explanation for the results, for example, socioeconomic factors were not adjusted for. This means that the researchers were unable to tease out the possibility that people who could afford to keep a pet might also be those whose children were less likely to get or report respiratory infections.
• The study only included children growing up in rural or suburban environments in Finland. The effect of dog contact may not be the same in children growing up in urban environments. 
• It is possible that parents of children who are allergic or whose previous children were allergic avoid keeping pets. Although the authors acknowledge that predictions based on data on pet keeping are not straightforward, this is one possibility they could not rule out.

In addition, how dogs may have a protective effect has not been investigated.