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Influenza B Virus Infection

Influenza B virus is a less common but still important cause of influenza infection, that is seen throughout the world. The clinical presentation is similar to all other human influenza viruses - fever, chills, cough, rhinitis, pharyngitis, and other constitutional symptoms. Because various complications can arise (most notably secondary bacterial pneumonia), an early diagnosis is imperative. In addition to a complete laboratory workup, various microbiological studies can be employed to confirm an influenza B virus infection.


Even though the "flu" has largely been attributed to the influenza A virus in terms of causality, the influenza B virus is responsible for approximately 20% of all cases [1] [2]. Similarly to influenza A, the influenza B virus prevails globally, but it primarily causes large epidemics and not pandemics, as is the case with influenza A [3]. In the majority of the cases, an influenza B virus infection causes a mild acute respiratory infection, characterized by a sudden onset of fever, chills, myalgia, headaches, and cough [2] [4]. Other notable complaints (particularly in the pediatric population) are pharyngitis, rhinitis, and asthenia, whereas gastrointestinal irritation, conjunctivitis, earache, and lymphadenopathy might also be encountered [2]. These manifestations persist for about a week, although constitutional symptoms can last more [3]. In rare cases, complicated infections may arise, especially in those who suffer from chronic cardiorespiratory diseases or diabetes mellitus [3]. In infants and younger children, laryngotracheobronchitis can be potentially serious, whereas pneumonia (mainly secondary bacterial, but also primary viral) with hemoptysis, dyspnea, edema, and cyanosis is one of the most severe and possibly life-threatening complications [3]. Other studies report urinary tract infections and kidney damage, atrial fibrillation and myocarditis, as well as central nervous system (meningitis, encephalitis, seizures) abnormalities [4] [5] [6].

Intravenous Administration
Constitutional Symptom
  • The clinical presentation is similar to all other human influenza viruses - fever, chills, cough, rhinitis, pharyngitis, and other constitutional symptoms.[symptoma.com]
Atrial Septal Defect
  • A 48-years-old woman with trisomy 21 and ostium primum atrial septal defect was transferred from Cardiology to our Internal Medicine Department for severe pericardial effusion unresponsive to ibuprofen and colchicine.[ncbi.nlm.nih.gov]
Large Pericardial Effusion
  • Especially in autumn and winter periods, clinicians should include Influenza B virus infection on differential diagnosis of pericarditis with large pericardial effusion.[ncbi.nlm.nih.gov]
Severe Clinical Course
  • These results suggest that influenza B virus can cause a severe clinical course and should be considered as an etiologic factor for encephalitis.[ncbi.nlm.nih.gov]
  • In the majority of the cases, an influenza B virus infection causes a mild acute respiratory infection, characterized by a sudden onset of fever, chills, myalgia, headaches, and cough.[symptoma.com]
  • Your patient is a 29-year-old woman with headache and influenza B virus infection.[wwwnc.cdc.gov]
  • Be aware of these differences: Cold symptoms Flu symptoms Low or no fever High fever Sometimes a headache Headache (very common) Stuffy, runny nose Clear nose or stuffy nose Sneezing Sometimes sneezing Mild, hacking cough Cough, often becoming severe[stanfordchildrens.org]
  • What we see with the flu is a sudden fever above 38 degrees, along with headaches, chills, fatigue, aching muscles, sore throat, and dry cough — where a person can become bed bound,” explained Dr Amin Ali.[gulfnews.com]
  • Symptoms of flu include fever, headache, extreme tiredness, dry cough, sore throat, runny or stuffy nose, and muscle aches.[virology.ws]
Neurologic Manifestation
  • Abstract During a 29-month period, 11 (12%) of 92 hospitalized patients with influenza B virus infection presented neurologic manifestations, which included febrile seizure in 4 cases and encephalopathy/encephalitis in 7 cases.[ncbi.nlm.nih.gov]
  • Influenza B neurologic manifestations have been reported mainly in children.[wwwnc.cdc.gov]
  • […] condition. 5,6 We herein reported the neurologic manifestations of hospitalized children with influenza virus B infection.[journals.lww.com]
Cerebellar Ataxia
  • These complications were clinically diagnosed as confirmed encephalitis (4 patients), possible encephalitis (2 patients), and cerebellar ataxia (1 patient). Two of the patients died.[ncbi.nlm.nih.gov]
  • These complications were clinically diagnosed as confirmed encephalitis (4 patients), possible encephalitis (2 patients), and cerebellar ataxia (1 patient). Two of the patients died.[ncbi.nlm.nih.gov]
  • In the preceding 24 hours, headache, dysarthria, right side motor deficit, and vomiting developed. Results of CSF testing and cranial CT and MRI were unremarkable. The patient was given oseltamivir and mannitol.[wwwnc.cdc.gov]


Because of the numerous complications that may arise, physicians must conduct a thorough physical examination and obtain a detailed patient history in the presence of an acute respiratory infection, especially in the pediatric population. Firstly, the abrupt onset of symptoms in the typical period of the year (during the winter) is highly suggestive of influenza, something which must be further corroborated by laboratory studies. A complete blood count (CBC) mainly shows leukopenia, whereas creatine kinase (CK) levels might also be elevated if myalgia is reported [7]. As soon as sufficient evidence is raised to pursue a diagnosis of influenza B infection, several microbiological tests are available [8] [9]:

  • Direct methods - Viral cultures are one of the first methods used to isolate viral pathogens, yielding positive results within several days (shell vial cultivation can provide a result within 48 hours) [8]. However, newer methods have largely replaced cultivation due to practicality and faster turnaround times.
  • Serology - Various methods that use antibodies against influenza antigens as a marker of identification exist - direct fluorescent antibody testing (DFA, used to distinguish between influenza A and B virus), hemagglutination inhibition assay (HAI, mainly intended to determine the strain of influenza A), and enzyme-linked immunoabsorbent assay (ELISA, one of the most widely used tests that have a very high sensitivity/specificity in practice) [8]. Recent studies have revealed a europium nanoparticle-based immunoassay (ENIA) that uses a novel method of detection through monoclonal antibodies, which seems to be even more effective in determining the exact strain of influenza B, but also influenza A viruses [8] [9].
  • Molecular testing - Compared to current serological tests, polymerase chain reaction (PCR) and reverse transcriptase-PCR (RT-PCR) are the gold standard for identifying influenza virus infections, carrying the best rate of detection [8].
  • If patients with influenza virus infection manifest acute respiratory distress with total lung atelectasis, clinicians should consider plastic bronchitis and early bronchoscopy should be intervened.[ncbi.nlm.nih.gov]


  • The treatment was well tolerated and hematologic and clinical chemical tests revealed no toxicity. The estimated dose of ribavirin aerosol retained was about 2 g in 35.5 hr of treatment during the first 60 hr in the hospital.[ncbi.nlm.nih.gov]


  • Patients surviving fulminant acute myocarditis exhibit a favorable long-term prognosis, with good recovery of cardiac function, which reinforces the importance of adequate hemodynamic support in the acute phase of great cardiovascular instability.[pediatrics.imedpub.com]


  • Based on the recent patient history of flu-like syndrome, and presence of pleuro-pericardial effusion, a viral etiology was suspected. Laboratory evaluation and molecular assay of tracheal aspirate identified influenza B virus.[ncbi.nlm.nih.gov]
  • Etiologic agents of viral myocarditis include enterovirus, adenovirus, parvovirus, hepatitis C virus, human immunodeficiency virus, influenza, and others.[pediatrics.imedpub.com]
  • Influenza B virus should be considered as an etiologic factor in encephalitis in adults as well as in children and adolescents 2.[wwwnc.cdc.gov]


  • Abstract Many aspects of the biology and epidemiology of influenza B viruses are far less studied than for influenza A viruses, and one of these aspects is efficacy and resistance to the clinically available antiviral drugs, the neuraminidase (NA) inhibitors[ncbi.nlm.nih.gov]
  • This test should not be performed unless the patient meets clinical and epidemiologic criteria for testing.[mayomedicallaboratories.com]
  • In particular, we find significant differences in the evolutionary and epidemiological dynamics between the Victoria and Yamagata lineages ( Table 3 ).[elifesciences.org]
  • "Combining information about the evolution of the virus with epidemiological data will generate disease forecasts before the season begins, significantly earlier than what is currently possible," said Mercedes Pascual, PhD, professor of ecology and evolution[sciencedaily.com]
Sex distribution
Age distribution


  • Suggests clinical disorders or settings where the test may be helpful Rapid and accurate detection of influenza A, influenza B, and respiratory syncytial virus in a single test for nasopharyngeal swab specimens Clinical Information Discusses physiology, pathophysiology[mayomedicallaboratories.com]
  • Although the pathophysiology of viral myocarditis has been studied in experimental models and limited in human myocardial tissue, it is known that the inflammatory reaction in myocarditis of viral etiology is due to the direct damage caused by the virus[pediatrics.imedpub.com]


  • Acute respiratory infections are one of the leading causes of death in children and adults, and influenza is among the few respiratory infections that can be prevented and treated by vaccination and antiviral treatment.[ncbi.nlm.nih.gov]



  1. Caini S, Huang QS, Ciblak MA, et al. Epidemiological and virological characteristics of influenza B: results of the Global Influenza B Study. Influenza Other Respir Viruses. 2015;9(1):3-12.
  2. Mosnier A, Caini S, Daviaud I, et al. Clinical Characteristics Are Similar across Type A and B Influenza Virus Infections. Schanzer DL, ed. PLoS One. 2015;10(9):e0136186.
  3. Taubenberger JK, Morens DM. The Pathology of Influenza Virus Infections. Annual review of pathology. 2008;3:499-522.
  4. Popescu CP, Florescu SA, Lupulescu E, et al. Neurologic Complications of Influenza B Virus Infection in Adults, Romania. Emerg Infect Dis. 2017;23(4):574-581.
  5. Allen RJ, Koutsakos M, Hurt AC, Kedzierska K. Uncomplicated Cystitis in an Adult Male Following Influenza B Virus Infection. Am J Case Rep. 2017;18:190-193.
  6. Chang TY, Chao TF, Liu CJ, et al. The association between influenza infection, vaccination, and atrial fibrillation: A nationwide case-control study. Heart Rhythm. 2016;13(6):1189-1194.
  7. Wang CC, Chen PY, Wang JD, Liu FC, Huang FL, Lee CY. Clinical and laboratory analysis of influenza B infection in children in Taichung, Taiwan during the 2006-2007 flu season. Pediatr Neonatol. 2009;50(2):54-58.
  8. Vemula SV, Zhao J, Liu J, Wang X, Biswas S, Hewlett I. Current Approaches for Diagnosis of Influenza Virus Infections in Humans. Ploss A, ed. Viruses. 2016;8(4):96.
  9. Zhang P, Vemula SV, Zhao J, et al. A Highly Sensitive Europium Nanoparticle-Based Immunoassay for Detection of Influenza A/B Virus Antigen in Clinical Specimens. Loeffelholz MJ, ed. J Clin Microbiol. 2014;52(12):4385-4387.

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Last updated: 2019-06-28 09:58