Bacteria are carried by various 'media', which can include raw food, moist surfaces where bacteria have been left, our hands or skin and from coughing or sneezing (打喷嚏).
2018年12月四级真题（第三套）阅读 Section B
Unless you're sitting next to someone who is coughing or sneezing, you shouldn't worry too much about getting sick.
2019年12月四级真题（第三套）阅读 Section A
柯林斯高阶英汉双解学习词典释义
VERB
咳嗽
When you cough, you force air out of your throat with a sudden, harsh noise. You often cough when you are ill, or when you are nervous or want to attract someone's attention.
2. sudden expulsion of air from the lungs that clears the air passages; a common symptom of upper respiratory infection or bronchitis or pneumonia or tuberculosis