Why is my kid always sick?

With children seemingly suffering endless coughs and colds, what is “normal”?

Oliver is a 3 year old boy brought into the emergency department by his mum with a fever, runny nose and cough. This is the 5th or 6th episode he’s had in the past 3 months and he barely seems to recover in between. He is not too unwell with this episode, but they have been so frequent that his mum wanted to get him checked out in case there was something else going on.

The above is a frequent scenario in paediatric primary care. It has always been common to get these questions during the winter, but there seems to be a particular peak in these concerns now.

This post is to examine what is normal, what is not, and what is going on right now. Let’s go!

What’s normal?

There are a very large number of respiratory viruses which typically cause varying severity of illness. For adults these don’t usually cause problems, as their immune system is fully developed and has had multiple opportunities to practice fighting them off already, so they have good immune memory (adaptive immunity).

For young children, their immune system is still maturing and they will be encountering many of these viruses for the first time. That means they have not yet developed the same strength of adaptive immunity (through antibodies and T cells which recognise the specific virus) to prevent infection, or to stop them getting too sick once infected.

When you are first born, you get the privilege of being protected by your mums antibodies for around the first 6 months of life. These are transferred to you during the last trimester of pregnancy (specifically, an antibody called IgG) and offer some protection during a particularly vulnerable period.

There is then a natural nadir in immunity, which is lowest between 3 - 6 months (known as physiological immunodeficiency of infancy) when you have lost maternal antibodies and haven’t made many of your own. Your immune system keeps developing; for example it hasn’t developed full protection against encapsulated bacteria (such as Streptococcus pneumoniae) until age 2 - 5 years, and production of IgA (an antibody important for immunity at mucosal sites, like your mouth and nose) doesn’t reach adult levels until adolescence.

As such, it is completely normal for young children to suffer from a surprisingly large number of respiratory tract infections.

A prospective cohort study from Germany following children from birth until age 12, found children had an average of >3 episodes per year between age 0 and 2, with an upper limit of the “normal range”, being 11 episodes per year!

The amazingly named, “BIG-LoVE” study from Utah, performed regular swabbing of different household members to be tested for respiratory viruses, regardless of symptoms. Remarkably, across the whole study people would test positive for a virus in nearly a quarter of all weekly swabs provided - but for children under 5 years this was 50% of all weeks - they would test positive for a respiratory virus half of their lives!

A) Number of weeks with one or more viral detection per person over 1y by age group. B) Number of weeks with one or more viral detection in the household by number of children. Gruber et al. 2007

Only around half of these episodes were associated with symptoms, showing how common it can be to be infected with a respiratory virus and not even realise it.

According to a systematic review, common cold symptoms persist for longer than 10 days in 50% of children and longer than 15 days in 10% of children. Considering most of these episodes get truncated into the winter months, it’s easy to see how multiple coughs and colds all blend together without a break for weeks on end.

Duration of cough and cold symptoms in systematic review. Thompson et al. 2013

The upshot of this is that for young children especially, it is very normal to have lots and lots of respiratory virus infections. Not very fun for them, or their parents. But normal none-the-less.

What is not normal?

Concerns about infections in children tend to be provoked when there are signs of an underlying problem with the immune system, which the child may have been born with (congenital) or, more rarely, may have acquired through a disease process (acquired).

The signs of this are usually very different to the above. It would be very rare for these syndromes to come to our attention simply due to recurrent respiratory viruses with a normal, benign course.

Problems with the immune system would normally present with recurrent infections which are unusually severe, or involve organisms which would not normally cause infection in people with normally functioning immune systems. We call these “opportunistic” pathogens, and they include things like fungi such as Aspergillus or Pneumocystis jirovecii among others.

Children who had recurrent infections which were so severe they frequently required hospitalisation, or occurring with these more peculiar organisms would be the kind to prompt further investigation.

There are also some characteristic patterns of infection which might prompt investigation for specific underlying immune problems, but these do not consist of frequent, benign viral upper respiratory tract infections in infancy.

Why is there so much concern currently?

Things seem particularly bad at the moment for several reasons. Winter is always a time where more of these viruses circulate, but this winter is particularly bad. For a long period during the pandemic, many of these viruses stopped circulating altogether. Because so few people were catching them, there is less immunity among children (and indeed adults) then there would normally be, so more people are catching them now, including more children are catching them for the first time.

For the age group particularly prone to these viruses (children <5 years), most or all of their lives has been lived during the pandemic period where substantially lower rates of these viruses have been circulating. A lot of first exposures which might have otherwise happened over a few years are now happening within a much shorter timeframe.

Summary

It is normal for young children to have lots and lots of viral respiratory infections. There are currently more viruses circulating than usual as young children have been relatively unexposed during the pandemic period and are encountering many of them for the first time. We are rarely concerned about children suffering frequent viral respiratory infections which follow the normal course. We become concerned when infections are unusually severe or involve opportunistic organisms which would not normally cause infection in people with functioning immune systems.

For advice on when to tell if your young child is more unwell than they should be with a fever, I highly recommend the healthier together website.

For more on fever particularly, you can check out my previous post here.

Don't fear the fever