Severe viral or bacterial respiratory infections that occur in childhood can cause airway abnormalities that may set the stage for COPD in later life. While there is no concrete evidence that these infections cause COPD, they may worsen the condition. There is also evidence, although limited, that some infections contracted before age 2 (for example, pertussis, tuberculosis, or pneumonia) may be a significant factor in the later development of COPD. There is some question, however, whether the previous infection is the cause, or whether they are both related to another factor, such as low birth weight.