Influenza Clinical Presentation

  • Author: Robert W Derlet, MD; Chief Editor: Burke A Cunha, MD   more...
 
Updated: Mar 8, 2012
 

History

The presentation of influenza virus infection varies; however, it usually includes many of the symptoms described below. Patients with influenza who have preexisting immunity or who have received vaccine may have milder symptoms.

Abrupt onset of illness is common. Many patients with influenza are able to report the time when the illness began.

Fever may vary widely among patients, with some having low fevers (in the 100°F range) and others developing fevers as high as 104°F. Some patients report feeling feverish and a feeling of chilliness.

Sore throat may be severe and may last 3-5 days. The sore throat may be a significant reason why patients seek medical attention.

Myalgias are common and range from mild to severe.

Frontal/retro-orbital headache is common and is usually severe. Ocular symptoms develop in some patients with influenza and include photophobia, burning sensations, and/or pain upon motion.

Some patients with influenza develop rhinitis of varying severity, but it is generally not the chief symptom.

Weakness and severe fatigue may prevent patients from performing their normal activities or work. In some cases, patients with influenza may find activity difficult and may require bedrest.

Cough and other respiratory symptoms may be initially minimal but frequently progress as the infection evolves. Patients may report nonproductive cough, cough-related pleuritic chest pain, and dyspnea. In children, diarrhea may be a feature.

Acute encephalopathy has been associated with influenza A virus infection. In a case series of 21 patients, Steininger et al described clinical, cerebrospinal fluid (CSF), magnetic resonance imaging (MRI), and electroencephalographic (EEG) findings.[22] Clinical features included altered mental status, coma, seizures, and ataxia. Of patients who underwent further testing, most had abnormal CSF, MRI, and EEG findings.

The incubation period of influenza averages 2 days, but it may range from 1 to 4 days. Because of aerosol transmission, and the possibility (albeit less likely) of transmission by asymptomatic persons and contaminated surfaces, the patient may be unaware of exposure to the disease.[13]

H1N1 influenza

In the 2009-2010 H1N1 influenza pandemic, initial symptoms included high fever, myalgias, rhinorrhea, and sore throat. Nausea, diarrhea, and vomiting were also reported. For more information, see the article H1N1 Influenza (Swine Flu).

Avian influenza

The key history component that should prompt consideration of avian influenza as a possible diagnosis is exposure to sick, dead, or dying poultry or humans with avian influenza. Many cases involve close contact, such as plucking or gutting of dead birds, removing infected carcasses, or ingesting incompletely cooked bird meat or blood. Some patients have had no history of exposure to sick birds, suggesting that spread from asymptomatic birds is possible or that the virus can be transmitted environmentally on fomites.

The mean time from exposure to onset of illness is 2-4 days, but can be as long as 8 days.[23] About 94-100% of cases begin with a typical influenza syndrome, including high fever (temperature >38°C) and lower respiratory tract symptoms (cough and pleuritic pain). Headache, myalgia, and fatigue are also common.[24, 23]

Dyspnea is reported in 76-100% of cases.[23] Lower respiratory tract involvement appears to occur earlier with avian flu than with seasonal influenza. Dyspnea, shortness of breath, hoarseness, and copious sputum production may be presenting complaints.[12] The sputum is sometimes bloody.

Upper respiratory findings of sore throat or rhinorrhea occurred in only about half of confirmed cases.[23]

GI symptoms, including diarrhea, nausea, and abdominal pain, are common early complaints occurring in 10-50% of patients.[23] Nonbloody, watery diarrhea appears to be more common with avian flu than with human seasonal influenza.[12]

Encephalitis may occur.[25] Two persons in Vietnam presented with encephalitis only.[26]

The incidence of asymptomatic or mild cases is uncertain. Seroprevalence studies demonstrated exposure in poultry workers but little exposure to health care workers caring for patients with avian influenza.[24]

Next

Physical Examination

The general appearance varies among patients who present with influenza. Some patients appear acutely ill, with some weakness and respiratory findings, while others appear only mildly ill. Upon examination, patients may have some or all of the following findings:

  • Fever of 100-104°F; fever is generally lower in elderly patients than in young adults
  • Tachycardia, which most likely results from hypoxia, fever, or both
  • Pharyngitis - Even in patients who report a severely sore throat, findings vary from minimal infection to more severe inflammation
  • Eyes may be red and watery
  • Skin may be warm-to-hot, as reflected by the temperature status. Patients who have been febrile with poor fluid intake may show signs of mild volume depletion with dry skin
  • Pulmonary findings during the physical examination may include dry cough with clear lungs or rhonchi
  • Nasal discharge is absent in most patients

Avian influenza

High fever (temperature >38°C), tachypnea, and hypoxia may be noted at presentation. Pulmonary rales may be heard early. Wheezes are occasionally apparent. Patients typically have a productive cough, occasionally with blood-tinged sputum.

Diarrhea is relatively common. Abdominal pain and vomiting are relatively infrequent.

Signs of upper respiratory tract infection, including coryza, conjunctivitis, and pharyngitis, may be noted, but these findings are not necessarily present. Conjunctivitis appears to be less common with H5N1 infection than with seasonal influenza or with infection due to other strains of avian influenza in humans. Case reports have described other occasional signs (eg, bleeding gums, always in the presence of viral pneumonia).[26]

Complications

Primary influenza pneumonia is characterized by progressive cough, dyspnea, and cyanosis following the initial presentation. Chest radiographs show bilateral diffuse infiltrative patterns, without consolidation, which can progress to a presentation similar to acute respiratory distress syndrome (ARDS).

Risks for viral pneumonia involve numerous complex host immune responses and viral virulence. Women in the third trimester of pregnancy are at higher risk, as they are for other complications of influenza A and B. Elderly individuals, especially nursing home patients, and those with cardiovascular disease usually constitute the highest risk groups; however, particular influenza strains may target younger persons. For example, in the 1918-1919 epidemic, many young adults died of a pneumonia that some experts believe was caused directly by the virus.

Secondary bacterial pneumonia can occur from numerous pathogens (eg, Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae). The most dreaded complication is staphylococcal pneumonia, which develops 2-3 days following the initial presentation of viral pneumonia. Patients appear severely ill, with hypoxemia, an elevated WBC count, productive bloody cough, and a chest radiograph showing multiple cavitary infiltrates.

A study from Israel compared H1N1 to non-H1N1 bacteremia in children and adults. Results show significant increases in S areus and S pyogenes infections in both groups during pandemic H1N1 influenza seasons. The highest increase was in S pneumoniae infections among children. There was not a marked increase in S pneumonia among adults.[27]

Methicillin-susceptible S aureus( MSSA) and methicillin-resistant S aureus (MRSA) pneumonias have occurred following influenza pneumonia. MRSA pneumonia may be severe and difficult to treat, and deaths have occurred within 24 hours of presentation of pneumonia symptoms.

S pneumoniae or H influenzae pneumonia, if occurring as a complication, usually develops 2-3 weeks after the initial symptoms of influenza and can be managed as a community-acquired pneumonia, following standard antibiotic and admission/discharge guidelines.

Myositis is a rare complication. This group of patients may develop frank rhabdomyolysis, with elevated creatine kinase levels and myoglobinuria. Myocarditis and pericarditis have been associated with influenza infections.

A review of avian influenza cases in 4 countries found that the clinical course progressed to ARDS and respiratory failure in 70-100% of patients.[24] The mean time to the development of ARDS was 6 days. Lymphopenia at presentation is a significant predictor of the progression to ARDS and death.[28]

Severe cases of avian influenza may progress to multiorgan failure. In a study of 12 hospitalized patients with confirmed H5N1 influenza, 75% had respiratory failure, 42% had cardiac failure, and 33% had renal failure.[24]

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Contributor Information and Disclosures
Author

Robert W Derlet, MD  Professor of Emergency Medicine, University of California at Davis School of Medicine; Chief Emeritus, Emergency Department, University of California at Davis Health System

Robert W Derlet, MD is a member of the following medical societies: American Academy of Emergency Medicine, American Association for the Advancement of Science, Infectious Diseases Society of America, Society for Academic Emergency Medicine, and Wilderness Medical Society

Disclosure: Nothing to disclose.

Coauthor(s)

Nicholas John Bennett, MB, BCh, PhD,  Assistant Professor in Pediatrics, Division of Infectious Diseases, Connecticut Children's Medical Center

Nicholas John Bennett, MB, BCh, PhD, is a member of the following medical societies: Alpha Omega Alpha and American Academy of Pediatrics

Disclosure: Nothing to disclose.

Ethan E Bodle, MD, MPH  Associate Physician, Department of Emergency Medicine, Kaiser Permanente East Bay Medical Center

Ethan E Bodle, MD, MPH is a member of the following medical societies: American College of Emergency Physicians and American Public Health Association

Disclosure: Nothing to disclose.

Joseph Domachowske, MD  Professor of Pediatrics, Microbiology and Immunology, Department of Pediatrics, Division of Infectious Diseases, State University of New York Upstate Medical University

Joseph Domachowske, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics, American Society for Microbiology, Infectious Diseases Society of America, Pediatric Infectious Diseases Society, and Phi Beta Kappa

Disclosure: Nothing to disclose.

Jon Mark Hirshon, MD, MPH  Associate Professor, Department of Emergency Medicine, University of Maryland School of Medicine

Jon Mark Hirshon, MD, MPH is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Emergency Physicians, American Public Health Association, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Edmond A Hooker II, MD, DrPH, FAAEM  Assistant Professor, Department of Emergency Medicine, University of Cincinnati College of Medicine; Associate Professor, Department of Health Services Administration, Xavier University

Edmond A Hooker II, MD, DrPH, FAAEM is a member of the following medical societies: American Academy of Emergency Medicine, American Public Health Association, Society for Academic Emergency Medicine, and Southern Medical Association

Disclosure: Nothing to disclose.

Hien H Nguyen, MD, MS  Associate Clinical Professor, Division of Infectious Diseases and Pulmonary/Critical Care Medicine, Infectious Diseases Consultant and Hospitalist, University of California, Davis, Health System; Medical Director, Acute Infections Management Service, Antimicrobial Infusion Service; Medical Director, Electronic Health Records of University of California, Davis, Health System

Hien H Nguyen, MD, MS is a member of the following medical societies: American College of Physicians, Infectious Diseases Society of America, and Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Frederick Burton Rose, MD, FACP  Professor, Department of Medicine, University Hospital Epidemiologist, State University of New York Upstate Medical University

Frederick Burton Rose, MD, FACP is a member of the following medical societies: American College of Physicians and Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Christian E Sandrock, MD, MPH, FCCP  Associate Professor of Clinical Medicine, Division of Pulmonary/Critical Care Medicine, Division of Infectious Diseases, Department of Internal Medicine, University of California, Davis Medical Center

Christian E Sandrock, MD, MPH, FCCP is a member of the following medical societies: American College of Chest Physicians, American Thoracic Society, and Infectious Diseases Society of America

Disclosure: Pfizer Honoraria Speaking and teaching; Pfizer Honoraria Consulting; therevance Honoraria Consulting; GSK Honoraria Speaking and teaching

David Yew, MD  Assistant Clinical Professor, Department of Surgery, University of Hawaii, John A Burns School of Medicine; Medical Director and Flight Physician, Hawaii Life Flight, AirMed International

David Yew, MD is a member of the following medical societies: Air Medical Physician Association and American College of Emergency Physicians

Disclosure: Nothing to disclose.

Specialty Editor Board

Klaus-Dieter Lessnau, MD, FCCP  Clinical Associate Professor of Medicine, New York University School of Medicine; Medical Director, Pulmonary Physiology Laboratory; Director of Research in Pulmonary Medicine, Department of Medicine, Section of Pulmonary Medicine, Lenox Hill Hospital

Klaus-Dieter Lessnau, MD, FCCP is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, American Medical Association, American Thoracic Society, and Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD  Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Joseph F John Jr, MD, FACP, FIDSA, FSHEA  Clinical Professor of Medicine, Molecular Genetics and Microbiology, Medical University of South Carolina College of Medicine; Associate Chief of Staff for Education, Ralph H Johnson Veterans Affairs Medical Center

Disclosure: Nothing to disclose.

Charles V Sanders, MD  Edgar Hull Professor and Chairman, Department of Internal Medicine, Professor of Microbiology, Immunology and Parasitology, Louisiana State University School of Medicine at New Orleans; Medical Director, Medicine Hospital Center, Charity Hospital and Medical Center of Louisiana at New Orleans; Consulting Staff, Ochsner Medical Center

Charles V Sanders, MD is a member of the following medical societies: Alliance for the Prudent Use of Antibiotics, Alpha Omega Alpha, American Association for the Advancement of Science, American Association of University Professors, American Clinical and Climatological Association, American College of Physician Executives, American College of Physicians, American Federation for Medical Research, American Foundation for AIDS Research, American Geriatrics Society, American Lung Association, American Medical Association, American Society for Microbiology, American Thoracic Society, American Venereal Disease Association, Association for Professionals in Infection Control and Epidemiology, Association of American Medical Colleges, Association of American Physicians, Association of Professors of Medicine, Infectious Disease Society for Obstetrics and Gynecology, Infectious Diseases Society of America, Louisiana State Medical Society, Orleans Parish Medical Society, Royal Society of Medicine, Sigma Xi, Society of General Internal Medicine, Southeastern Clinical Club, Southern Medical Association, Southern Society for Clinical Investigation, and Southwestern Association of Clinical Microbiology

Disclosure: Nothing to disclose.

Chief Editor

Burke A Cunha, MD  Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital

Burke A Cunha, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, and Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Additional Contributors

The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous author Ruth Lawrence, MD, to the development and writing of the source article.

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Chest radiograph of severe lung disease in a patient with avian influenza.
Global map of countries where avian influenza (bird and human infections) has been reported. Image courtesy of PandemicFlu.gov.
Colorized transmission electron micrograph shows avian influenza A H5N1 viruses (gold) grown in MDCK cells (green). Image courtesy of Centers for Disease Control and Prevention.
Transmission electron micrograph (original magnification 150,000X) shows ultrastructural details of an avian influenza A (H5N1) virion, a subtype of avian influenza A. Note the stippled appearance of the roughened surface of the proteinaceous coat encasing the virion. Image courtesy of Centers for Disease Control and Prevention.
Photograph shows police officers during the 1918 Spanish flu pandemic. Image courtesy of US National Archives.
Avian H5N1 influenza in humans, annual case counts from the World Health Organization.
 
 
 
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