Unexplained lung infections can be done invasively when necessary to identify the causative organisms of the infection. The common causative agents of lung infections are viruses, bacteria, mycoplasma, chlamydia, fungi, parasites, etc. Sputum culture, blood culture, bacterial and fungal tests, as well as virus tests, mycoplasma and chlamydia antibody tests can be performed to clarify the causative agent. If the causative organism is not yet clear, anti-infection treatment with antibiotics can be selected empirically first, if the anti-infection treatment is less effective and the microbial test results are negative. If the anti-infective treatment is ineffective and the microbiological test is negative, it will be difficult to treat the disease. All of the above tests are invasive and may have certain complications and need to be performed on a trade-off basis depending on the condition.