看一下中国的一些讨论。一般是引用马里兰大学一个教授的试验。

https://www.thepaper.cn/newsDetail_forward_5872421

下面有这个试验的摘要。

我简单看了一下这个研究项目。收集的呼吸气中病毒，是要求参加试验的病人坐30分钟，通过一个紧套在病人面部上的设备收集。

142个病人，有218个样品。52个发现病毒。如果这样，应该是23.9%，而不是下面的39%。或者是52个病人的样品中发现病毒？

其实，对这个研究项目的设计是有问题的。如果怀疑正常呼出气中有病毒，不需要坐30分钟收集。只要放在鼻子下收集就可以了。对于流感患者，坐30分钟，很可能会有喷嚏或咳嗽，这样收集到的呼吸气事实上就不是正常的呼吸气了。由于并不是所有或大部分呼吸气样品都有病毒，更说明，正常呼吸气中大部分情况应该并没有病毒。

AAbstract

Little is known about the amount and infectiousness of influenza virus shed into exhaled breath. This contributes to uncertainty about the importance of airborne influenza transmission. We screened 355 symptomatic volunteers with acute respiratory illness and report 142 cases with confirmed influenza infection who provided 218 paired nasopharyngeal (NP) and 30-minute breath samples (coarse >5-µm and fine ≤5-µm fractions) on days 1–3 after symptom onset. We assessed viral RNA copy number for all samples and cultured NP swabs and fine aerosols. We recovered infectious virus from 52 (39%) of the fine aerosols and 150 (89%) of the NP swabs with valid cultures. The geometric mean RNA copy numbers were 3.8 × 104/30-minutes fine-, 1.2 × 104/30-minutes coarse-aerosol sample, and 8.2 × 108 per NP swab. Fine- and coarse-aerosol viral RNA were positively associated with body mass index and number of coughs and negatively associated with increasing days since symptom onset in adjusted models. Fine-aerosol viral RNA was also positively associated with having influenza vaccination for both the current and prior season. NP swab viral RNA was positively associated with upper respiratory symptoms and negatively associated with age but was not significantly associated with fine- or coarse-aerosol viral RNA or their predictors. Sneezing was rare, and sneezing and coughing were not necessary for infectious aerosol generation. Our observations suggest that influenza infection in the upper and lower airways are compartmentalized and independent.