After exclusion of pulmonary illnesses such as infection, cancer, foreign body aspiration, cystic fibrosis, alveolitis, asthma, and chronic obstructive pulmonary disease (COPD), the remaining explanations for chronic cough include medication with angiotensin-converting enzyme (ACE) inhibitor, gastroesophageal reflux disease (GERD), and post-nasal drip. This evidence concerns the gene ACE and infection.