Influenza pneumonia is a life-threatening complication of influenza virus infection, one of the most frequently encountered infections in clinical practice. After typical symptoms of upper respiratory tract infection and fever appear, severe respiratory decline with hypoxia and cyanosis can ensue without early recognition and appropriate therapy. Several diagnostic tests exist for prompt confirmation of influenza infection, but clinical suspicion is the key to diagnose the condition.
Presentation
Influenza is a rather common viral upper respiratory tract infection among humans. It is caused by influenza A (and less commonly B) viruses, and the pathogenesis, as well as transmission, involves several animal hosts and human-to-human spread through air droplets via inhalation, coughing, or sneezing [1] [2]. After an incubation period of a few days, constitutional symptoms of myalgia, fatigue, malaise, anorexia, fever, and a dry cough are main manifestations of influenza infection and usually last for 7-10 days [1] [3] [4]. It must be noted that the majority of infections are seen during the winter, and rarely in other parts of the year when pandemic or epidemic outbreaks occur [1] [2] [4]. In some patients, the infection is self-limiting, but numerous complications may arise, one of them being influenza pneumonia [1] [2] [3] [4] [5] [6]. It is regarded as the most severe complication and appears more frequently in the presence of various risk factors [5]. In children, concomitant cardiorespiratory illnesses (eg. asthma), diabetes mellitus, immunosuppression, long-term use of aspirin, and other diseases that increase the risk of hypertension are well-established risk factors, whereas pregnancy, chronic diseases, obesity, and residency in chronic care facilities are strongly associated with the development of influenza complications in adults and the elderly [2] [4] [5]. Influenza pneumonia represents the dissemination of the virus into the lower respiratory tract and the lung parenchyma, but secondary bacterial infections of the lungs might also be the culprit in influenza-infected patients, as the virus indirectly promotes bacterial adhesion to the respiratory epithelium [1] [2] [4] [5] [7]. For this reason, a clear distinction between primary influenza pneumonia and secondary bacterial pneumonia may be difficult to make. Nevertheless, approximately 2-5 days after the appearance of signs and symptoms typical for influenza, dyspnea, hypoxia, hemoptysis, cyanosis, and rapidly ensuing acute respiratory distress are hallmarks of influenza pneumonia [2] [3] [4] [8]. In addition, cognitive impairment, gastrointestinal complaints (diarrhea, abdominal pain) and myalgia are reported, and are sometimes the only symptoms, particularly in the elderly population [6]. In fact, pneumonia is one of the most important causes of death from this viral infection, and fatal outcomes might be seen within 24 hours [3] [5] [8] [9].
Workup
Mortality rates of influenza pneumonia are very high without early therapy, thus a detailed and comprehensive clinical, radiological, and microbiological assessment is vital in preventing the onset of respiratory decline. Firstly, physicians must obtain a complete patient history that will note the course and progression of symptoms and reveal any preexisting comorbidities that could predispose patients to a more severe form of infection. The physical examination is important in guiding the physician toward the lungs as the primary source of infection, after which both imaging studies and microbiological evaluation are necessary. Plain radiography is a valuable tool for visualizing the changes in the lung parenchyma for many infections, including influenza, and bilateral reticular or reticulonodular opacities, as well as patchy areas of consolidation (although other authors suggest that consolidation is absent) are principal features of influenza pneumonia [2] [3] [5] [9]. Unfortunately, not all patients exhibit typical X-ray findings [6]. Thus, confirmation of influenza virus as the underlying cause through microbiological testing is crucial. Several tests are available [1] [2] [5] [6]:
- Rapid influenza diagnostic test (RIDT) - Very fast results (within 15-30 minutes), the ability to discern between influenza A and B, and very high specificity are the reasons why RIDT is quite often performed in standard practice [1] [3] [4] [5].
- Reverse transcriptase-polymerase chain reaction (RT-PCR) - Although it is more expensive and requires advanced technical equipment, the RT-PCR test detects viral genetic material and possesses very high sensitivity and specificity rates [2] [5]. Because of its fast turnaround time (1-4 hours), it is considered to be the optimal diagnostic procedure [3] [5].
- Viral culture - Long waiting times (several days) are the main limitation of viral cultivation in the setting of influenza pneumonia, despite the fact that the specificity rate is virtually 100%. However, newly designed tests can yield conclusive results within 1-3 days [5].
- Serology - Detection of specific influenza antibodies is now being replaced by faster and more reliable methods for the diagnosis of influenza, and serology is often used as a retrospective analysis [5].
Treatment
Treatment for influenza pneumonia focuses on alleviating symptoms and addressing the underlying viral infection. Antiviral medications, such as oseltamivir (Tamiflu) or zanamivir (Relenza), are most effective when administered within 48 hours of symptom onset. Supportive care, including rest, hydration, and over-the-counter medications for fever and pain, is also important. In severe cases, hospitalization may be required for oxygen therapy or mechanical ventilation to support breathing.
Prognosis
The prognosis for influenza pneumonia varies depending on the patient's age, overall health, and the timeliness of treatment. While many individuals recover fully with appropriate care, the condition can be life-threatening, particularly for high-risk groups. Complications such as acute respiratory distress syndrome (ARDS) or secondary bacterial infections can worsen outcomes. Early diagnosis and treatment are key to improving prognosis.
Etiology
Influenza pneumonia is caused by the influenza virus, which is a highly contagious pathogen that spreads through respiratory droplets. The virus can infect the upper and lower respiratory tract, leading to inflammation and fluid accumulation in the lungs. There are several strains of the influenza virus, with types A and B being the most common causes of seasonal flu outbreaks.
Epidemiology
Influenza pneumonia is a global health concern, with seasonal outbreaks occurring primarily in the fall and winter months. The incidence of influenza pneumonia varies annually, influenced by factors such as viral strain virulence and vaccination rates. Certain populations, including the elderly, young children, pregnant women, and individuals with chronic health conditions, are at higher risk for developing severe illness.
Pathophysiology
The pathophysiology of influenza pneumonia involves the invasion of the influenza virus into the respiratory epithelium, leading to cell damage and an inflammatory response. This inflammation causes the alveoli (air sacs in the lungs) to fill with fluid, impairing gas exchange and resulting in respiratory distress. The immune response to the virus can further exacerbate lung damage, contributing to the severity of the condition.
Prevention
Preventing influenza pneumonia involves several strategies, with vaccination being the most effective. Annual flu vaccines are recommended for most individuals, particularly those in high-risk groups. Good hygiene practices, such as frequent handwashing and covering coughs and sneezes, can reduce the spread of the virus. Additionally, avoiding close contact with infected individuals and maintaining a healthy lifestyle can help bolster the immune system.
Summary
Influenza pneumonia is a serious respiratory condition caused by the influenza virus, characterized by symptoms of both flu and pneumonia. Prompt diagnosis and treatment are essential to prevent complications and improve outcomes. Vaccination and good hygiene practices are key preventive measures. Understanding the disease's presentation, workup, and management can aid in effective patient care.
Patient Information
For patients, it's important to recognize the symptoms of influenza pneumonia, which include high fever, cough, and difficulty breathing. If you experience these symptoms, especially if you are in a high-risk group, seek medical evaluation promptly. Vaccination is the best preventive measure, and maintaining good hygiene can help protect you and others from the virus. Remember, early treatment can significantly improve recovery chances.
References
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- Marzoratti L, Iannella HA, Gómez VF, Figueroa SB. Recent Advances in the Diagnosis and Treatment of Influenza Pneumonia. Curr Infect Dis Rep. 2012;14(3):275-283.
- Falsey AR, Walsh EE. Viral pneumonia in older adults. Clin Infect Dis. 2006;42(4):518-524.
- Joseph C, Togawa Y, Shindo N. Bacterial and viral infections associated with influenza. Influenza Other Respir Viruses. 2013;7(2):105-113.
- Rello J, Rodríguez A, Ibañez P, et al. H1N1 SEMICYUC Working Group. Intensive care adult patients with severe respiratory failure caused by Influenza A (H1N1)v in Spain. Crit Care. 2009;13:R148.
- Kim EA, Lee KS, Primack SL, et al. Viral pneumonias in adults: radiologic and pathologic findings. Radiographics. 2002;22 Spec No:S137-149.