Isolated neutropenia appears unlikely to require intervention

Abstract

Acetaminophen is a common symptomatic treatment for respiratory viral infections with fever. Early-life respiratory viral infections are associated with (not currently proven to cause) asthma development later in life. Concluding that early-life acetaminophen use causes later-life asthma exemplifies potential CBI. Acetaminophen may be indicated to treat fever, but it cannot, therefore, be concluded that it causes later-life asthma. CBI occurs when an exposure (acetaminophen) appears to be associated with an outcome (later-life asthma) but may be due to an indication (respiratory viral infection with fever) that led to the exposure (acetaminophen). CBI is a peril of observational studies. In many cases, randomized trials could mitigate CBI. However, as randomized trials are often impractical or unethical, one needs to be mindful of CBI when evaluating association studies. See the commentary to the Qiu et al study, below, for another example.