Table 2

Main categories of risk factors and biomarkers associated with general (undiagnosed) ARill, by category of risk and strength of each association

Main categories of risk factors and biomarkers assessed	Association identified	Strength	Confounders	Variables adjusted for (confounders/ multivariable model)	Study
Demographics factors
Age	No	0	–	No/No	Blume et al 28
Gender	No	0	–	No/No	Blume et al 28
Sport (type and level of participation)
Being at a less competitive level	Yes	+++	Age, age of menarche, no of inhabitants living in the same house	Yes/Yes	Novas et al 95
Being at a less competitive level	Yes	+	–	No/No	Matthews et al 87
Greater in runners	Yes	+	–	No/No	Ihalainen et al 92
Training and competition factors
Increased training load	Yes	+++	Subject (pre-exercise values), subject and session-intensity.	Yes/Yes	Novas et al 91
	Yes	+	–	No/No	Novas et al 95
	No	000	Training weeks and no of players	Yes/Yes	Tiernan et al 82
	No	0	–	No/No	Matthews et al 87
Intensified phase of training	Yes	+	–	No/No	Novas et al 91
Intensified phase of training	No	000	Training macrocycle, internal-TL values, well-being, muscle soreness ratings and age.	Yes/Yes	Thornton et al 89
Competition phase	No	000	Training macrocycle, internal-TL values, well-being, muscle soreness ratings and age.	Yes/Yes	Thornton et al 89
Nutritional factors
Lower (vitamin-D)	Yes	+++	Age, gender and years of training	Yes/Yes	Cox et al 39
Serum (vitamin-D) in both winter and summer	No	0	–	No/No	Scullion et al 52
Environmental/exposure factors
Winter	Yes	+	–	No/No	Scullion et al 52
Longer international travelling	Yes	+	–	No/No	Fowler et al 68
Household size	No	00	Age, age of menarche, no of inhabitants living in the same house	Yes/No	Novas et al 91
Immune/haematological risk factors and biomarkers
Elevated WBC counts	Yes	+++	Age, gender and years of training	Yes/Yes	Cox et al 39
Elevated neutrophil count	Yes	+++	Age, gender and years of training	Yes/Yes	Cox et al 39
Detection of IgE antibodies to aero-allergens	Yes	+	–	No/No	Reid et al 38
Detection of IgE antibodies to aero-allergens	No	000	Age, gender and years of training	Yes/Yes	Cox et al 39
Higher atopic AQUA scores	Yes	+	–	No/No	Ansley et al 93
Higher rates of expression of EBV-DNA in saliva (viral reactivation)	Yes	+	–	No/No	Reid et al 38
Lower resting and post-exercise (IL-1ra) in illness-prone athletes	Yes	+	–	No/No	Cox et al 88
High expression IL-2 genotype (GG)– lower incidence	Yes	+	–	No/No	Cox et al 32
Low expression IL-4 genotype (CC)	Yes	+	–	No/No	Cox et al 32
High expression IL-6 genotype (GG)	Yes	+	–	No/No	Cox et al 32
Low expression IL6 genotype (CC)	Yes	+	–	No/No	Zehsaz et al 31
Expression of IL-1ra, IL-8, IL-10, IFNɣ genotypes	No	0	–	No/No	Cox et al 32
Higher post-exercise (IL-6)	Yes	+	–	No/No	Cox et al 88
Lower resting (IL8) in illness-prone athletes	Yes	+	–	No/No	Cox et al 32
High expression IL-10 genotype (GG)	Yes	+	–	No/No	Zehsaz et al 31
Lower resting and post-exercise (IL-10) in illness-prone athletes	Yes	+	–	No/No	Cox et al 88
Changes in post-exercise (IL-2), (IL-4), (IL-12)	No	0	–	No/No	Cox et al 32
Reduction in salivary-AA, and IgM to total protein ratio	Yes	+	–	No/No	Ihalainen et al 92
Lower serum (IgG3)	Yes	+	–	No/No	Reid et al 38
Reduction in salivary-(Lysozyme)	No	0	–	No/No	Cunniffe et al 94
Reduction in salivary flow rate	No	000	Training weeks and no of players	Yes/Yes	Tiernan et al 82
Reduction in salivary flow rate	No	0	–	No/No	Nakamura et al 90

Strength of association; no association, 0; no association with multiple models and/or correction for confounders, (00/000); some association, +; good association, ++; strong association, +++.
AA, alpha amylase; AQUA, automated quantitative analysis; ARill, acute respiratory illness; EBV, Epstein-Barr Virus; WBC, white blood cell.