Severe Pneumonia Caused by Viruses: This includes, but is not limited to, severe pneumonia caused by infections such as respiratory syncytial virus, influenza virus, rhinovirus, human metapneumovirus, adenovirus, etc.; coronavirus is excluded. Diagnostic Criteria: Subjects with pneumonia caused by viral infections. According to the diagnostic criteria for adult community-acquired pneumonia (CAP) in China's 2018 primary care guidelines, a diagnosis of severe pneumonia can be made if one of the following main criteria or at least three secondary criteria are met. Main criteria: ① Need for endotracheal intubation for mechanical ventilation; ② Septic shock requiring vasopressors despite aggressive fluid resuscitation. Secondary criteria: ① Respiratory rate ≥30 breaths/min; ② Oxygenation index ≤250 mmHg (1 mmHg = 0.133 kPa); ③ Multilobar infiltrates; ④ Altered mental status and/or disorientation; ⑤ Blood urea nitrogen ≥7.14 mmol/L; ⑥ Systolic blood pressure \<90 mmHg requiring aggressive fluid resuscitation. Viral Detection Methods: The type or subtype of infecting virus is confirmed by nucleic acid testing of patient samples (oropharyngeal swabs, nasopharyngeal swabs, nasopharyngeal aspirates, tracheal aspirates, sputum, and other respiratory specimens, blood samples). Severe pneumonia (SP) is a serious respiratory disease that has emerged globally in recent years, with complex pathogenesis and difficult treatment. Due to different causes, different pathogens, and different situations leading to lung tissue (bronchioles, alveoli, interstitium) inflammation, there are similar or identical pathophysiological processes. When they develop to a certain stage of the disease, they can all worsen and become SP, causing organ dysfunction or even threatening life . SP is associated with high mortality (short-term and long-term) and pulmonary and extrapulmonary complications. Proper diagnosis and early initiation of adequate antimicrobial treatment for patients with severe pneumonia are key to improving the survival rate of critically ill patients. Viral pneumonia is an acute inflammation of the terminal airways, alveolar cavities, and/or interstitium of the lungs caused by viral infections, often resulting from the downward spread of upper respiratory tract infections. It is more common in winter and spring, and can be sporadic, epidemic, or explosive. Viral pneumonia often causes varying degrees of hypoxia and infection symptoms in the body, usually manifesting as fever, cough, wheezing, shortness of breath, and moist rales in the lungs, along with abnormalities in chest imaging \[such as X-rays, computed tomography (CT), etc.\]. Common pathogens include influenza A virus, parainfluenza virus, adenovirus, coronavirus, coxsackievirus, cytomegalovirus, respiratory syncytial virus, measles virus, varicella virus, etc. The imaging manifestations of viral pneumonia are diverse, but the lesions are often multiple and diffuse, distributed along the periphery and around bronchovascular bundles, with early presentations of multiple small patchy shadows and interstitial changes, thickening of the interlobular and intralobular septa; as the disease worsens, it manifests as multiple ground-glass opacities, which can progress to patchy, nodular, or large confluent consolidations . Typically, viruses from the same virus family have similar pathogenic mechanisms, hence the imaging of viral pneumonia they cause is similar. In terms of pathological characteristics, different severe viral pneumonias also share commonalities . The main manifestations are histological patterns of acute interstitial pneumonia changes, with or without diffuse alveolar damage. Grossly: Lung tissue is enlarged in volume and increased in weight due to congestion and edema (varying with the degree of lesions), with hemorrhagic areas appearing purplish red, and milder lesions may not be apparent. Microscopically: The lesions can be roughly divided into early, middle, late, and terminal stages. Viral severe pneumonia is aggressive in onset, initially presenting with fever, cough, and rhinorrhea; it then rapidly progresses to severe toxic symptoms, with respiratory manifestations including cough and dyspnea, producing white mucoid sputum, purulent sputum, or pink frothy sputum. Wheezing is a significant feature that distinguishes viral pneumonia from bacterial pneumonia, often accompanied by shortness of breath and fever, with severe cases potentially exhibiting lower chest wall inspiratory retractions, perioral cyanosis, and nasal flaring. Physical examination of the lungs often reveals fine to medium moist rales and expiratory wheezing sounds. Chest X-rays may show interstitial infiltrates, patchy shadows, and increased transparency in both lungs, with potential atelectasis. Peripheral blood white blood cell counts are mostly normal, with neutrophil proportions not high, and in cases of bacterial coinfection, white blood cell and neutrophil counts increase. C-reactive protein (CRP) can be normal or slightly elevated. Severely ill patients are often in a critical state of life, endangering the patient's circulatory system, and are in a state of respiratory failure requiring ventilator support. Active treatment of viral severe pneumonia, with appropriate measures, can lead to complete recovery of pulmonary function. If respiratory failure or poor circulatory function occurs and ultimately cannot be corrected, the prognosis is poor. In recent years, new viruses such as the H1N1 influenza virus, H7N9 avian influenza virus, SARS coronavirus (SARS CoV), and Middle East respiratory syndrome coronavirus (MERS-CoV) have emerged as new public health issues, leading to outbreaks or epidemics of viral pneumonia on a global or regional scale.
