In recent years, there is increasing interest in determining linkages between mental health in early life and risk of poor mental health in adolescence and adulthood [1–5]. Literature to date generally supports a relationship between mental health and early behavioral tendencies and mental health status and psychiatric outcomes later in life. More recently, there is growing interest in extending this link by investigating whether and to what degree physical health in early life is predictive of later mental health and functional outcomes [5, 6]. In particular, there has been growing interest in the linkages between early immune functioning and later health outcomes [7–9].
Previous clinical and epidemiologic data have demonstrated links between early immune functioning and later physical health outcomes [10–12]. In general, severe infection has been shown to be associated with increased risk of physical health problems in adolescence and later adulthood. For instance, youth with early respiratory infections have increased risk of respiratory disease (e.g., asthma) in later life [13–15]. Yet, this is not the outcome in all cases, and severity of early insult/illness may play a significant role in this determination.
More recently, there are converging data from several sources suggesting that infection early in life may also be related to poor mental health outcomes. For instance, data from adult cross-sectional epidemiologic samples showing higher rates of schizophrenia and other psychotic disorders among those exposed to early infection [16–18]. More recently, this link has been extended to anxiety disorders among youth [19–23]. Specifically, there is increasing evidence of a relationship between infection early in life and increased likelihood of anxiety disorders later in childhood and adulthood. This association is supported by evidence from two sources. First, there are data to suggest an association between streptococcal infection and increased risk of obsessive-compulsive disorder (OCD) in clinical samples [20–23]. Second, data from community-based samples suggest that there is a relationship between early respiratory disease and increased risk of panic-related disorders during young adulthood .
There are also convergent data from laboratory studies suggesting that infection may lead to changes in immune function (e.g., shift from T1 to T2 immune functioning) and that these may relate to increased depressive symptoms and behaviors [24–26].
In sum, there is growing interest and evidence regarding an association between infection early in life and increased risk of later poor mental health outcomes. Yet, several questions remain unanswered. First, it is not known whether there is an association between early infection and increased risk of any mental disorders, or if the risk specific to only some disorders. Second, it is not clear whether the association between early infection and later increased risk of mental disorders applies to the community, or whether it is only evident in selected clinical samples.
Against this background, the goal of the current study is to determine the association between infection early in life and the risk of mental disorders among youth in the community. The study will: (1) investigate the association between early infection and the odds of any mental disorders in youth, compared to youth without early infection; (2) investigate the association between early infection and specific mental disorders in youth, compared with those without early infection.