How many respiratory infections in children are "normal" per year?

Respiratory infections are the most frequent illness in childhood.

How many respiratory infection episodes can be expected in a normal child?

According to a German study of 760 children followed for 12 years, the mean cumulative number of respiratory infections up to age 12 yr was 22. In infancy, the mean annual number was 3.4 episodes; at pre-school age, 2.3 episodes; and at school, age 1.1 episodes.

Based on a two-fold standard deviation of the mean, the number of "normal" respiratory infections was up to:

- 11 respiratory infection episodes per year in infancy
- 8 episodes per year at pre-school age
- 4 episodes per year at school age

Episodes within these reference values should not cause unwarranted concerns of suspected immunodeficiency.



References:

History of respiratory infections in the first 12 yr among children from a birth cohort. Christoph Grüber et al. Pediatric Allergy and Immunology (OnlineEarly Articles).
doi:10.1111/j.1399-3038.2007.00688.x
Why children with asthma get sick in September?
Allergic sensitization is associated with rhinovirus-, but not other virus-, induced wheezing in children. http://goo.gl/PghX
Most Helpful Warning Signs to Identify Primary Immunodeficiency Diseases - Medscape, 2011.
Rhinoviruses: markers of, or causative for, recurrent wheeze and asthma? ERJ 2012.
Image source: Molecular surface of a rhinovirus, Wikipedia, GNU Free Documentation License.

Comments from Twitter:

Nazım Coşkun @nazimcoskun: I am not sure if 11 respiratory infection episodes per year in infancy should not cause concerns of immunodeficiency.

@Allergy: agree, that's why I've embedded the PDF with "10 warning signs for PIDD" at the end: http://goo.gl/LMZ7