{
 "topic": "Influenza A",
 "slug": "influenza-a",
 "category_id": 15765,
 "passage_count": 14,
 "source_chars": 12700,
 "enough_material": true,
 "references": [
  {
   "title": "Pediatric Board Study Guide",
   "author": null,
   "pages": [
    272
   ]
  },
  {
   "title": "Red Book Atlas of Pediatric Infectious Diseases",
   "author": "American Academy of Pediatrics,Carol J. Baker, MD, FAAP",
   "pages": [
    302,
    306,
    348
   ]
  },
  {
   "title": "CURRENT Diagnosis and Treatment Pediatrics, Twenty-Fourth Edition",
   "author": "Hay, William W., Levin, Myron J., Deterding, Robin R., Abzug, Mark J.",
   "pages": [
    1227
   ]
  },
  {
   "title": "Kliegman R. Nelson Textbook of Pediatrics 2-Volume Set 22ed 2024",
   "author": null,
   "pages": [
    2028,
    2029,
    2030,
    2587
   ]
  },
  {
   "title": "Fever without a source in children 3 to 36 months of age: Evaluation and management - UpToDate",
   "author": null,
   "pages": [
    2
   ]
  },
  {
   "title": "Red_Book_2021_2024_Report_of_the_Comm_z_library_sk,_1lib_sk,",
   "author": null,
   "pages": [
    497
   ]
  },
  {
   "title": "Cover",
   "author": "Vitalsource Download",
   "pages": [
    3599
   ]
  },
  {
   "title": "MedStudy Pediatrics Core 11th Edition 2024-2025",
   "author": null,
   "pages": [
    800
   ]
  }
 ],
 "passages": [
  {
   "source": "Pediatric Board Study Guide, p. 272",
   "text": "- Most recent pandemic: 2009\u20132010 caused by influenza A (H1N1) - Mode of transmission - Large-particle respiratory droplet between individuals (cough and sneeze) - Contact with contaminated surfaces; fingers then touch face - \u2013 Incubation period is 1\u20134 days - Most outbreaks occur in schools - Hospitalization rates are highest in children <2 years and elderly >65 years ## **Clinical presentation** - Fever, malaise, myalgia, headache, nonproductive cough, sore throat, and rhinitis - Children may also develop croup or bronchiolitis - Younger children may have febrile seizures or sepsislike symptoms - Uncomplicated influenza disease typically resolves within 3\u20137 days ## **Complications** - Primary viral pneumonia - Secondary bacterial infections such as pneumonia ( _S. aureus_ and _S. pneumoniae_ ) - Sinusitis and otitis media - Encephalitis"
  },
  {
   "source": "Red Book Atlas of Pediatric Infectious Diseases, p. 302",
   "text": "## Etiology Influenza viruses are orthomyxoviruses of 3 genera or types (A, B, and C). Epidemic disease is caused by influenza virus types A and B, and influenza A and B virus antigens are included in influenza vaccines. Type C influenza viruses cause sporadic, mild influenza-like ill ness in children and antigens are not included in influenza vaccines. The virus type or subtype may have an effect on the number of hospitalizations and deaths that season. For example, seasons with influenza A (H3N2) as the predominant circulating strain have had 2.7-times higher average mortality rates than other seasons. The 2009 influenza A (H1N1) pandemic combined exceptional pediatric virulence and lack of immunity, which resulted in nearly 4 times as many pediatric deaths as usually recorded."
  },
  {
   "source": "CURRENT Diagnosis and Treatment Pediatrics, Twenty-Fourth Edition, p. 1227",
   "text": "- \u00bb Detection of virus, viral antigens, or nucleic acid in respiratory secretions. Symptomatic infections are common in children because they lack immunologic experience with influenza viruses. Infection rates in children are greater than in adults and are instrumental in initiating community outbreaks. Epidemics occur in fall and winter. Three main types of influenza viruses (A/H1N1, A/H3N2, B) cause most human epidemics, with antigenic drift ensuring a supply of susceptible hosts of all ages. In recent years, avian influenza A/H5N1 and A/H7N9 caused isolated human outbreaks in Asia that were associated with high rates of hospitalization and death. A swine-origin influenza A/H1N1 caused a human pandemic in 2009 and 2010 and has since circulated with seasonal periodicity. An influenza A/H3N2v of swine origin has also caused clusters of human infections in the last 5 years in the United States, commonly associated with exposure to pigs. ## \u00bb **Clinical Findings**"
  },
  {
   "source": "Red Book Atlas of Pediatric Infectious Diseases, p. 306",
   "text": "Control of fever with acetaminophen or another appropriate nonsalicylate-containing antipyretic agent may be important in young children because fever and other symptoms of influenza could exacerbate underlying chronic conditions. Children and adolescents with influenza should not receive aspirin or any salicylate-containing products because of the potential risk of developing Reye syndrome. ![](/tmp/pdf-images/pdf-0306-11.png) Image 70.2 Colorized transmission electron micrograph of avian influenza A (H5N1) viruses (seen in gold) grown in madin-Darby canine kidney epithelial cells (seen in green). Avian influenza A viruses do not usually infect humans; however, several instances of human infections and outbreaks have been reported since 1997. When such infections occur, public health authorities monitor these situations closely. Courtesy of Centers for Disease Control and Prevention/Courtesy of Cynthia Goldsmith; Jacqueline Katz; Sherif r. Zaki. 299 iNFLuENZA"
  },
  {
   "source": "Kliegman R. Nelson Textbook of Pediatrics 2-Volume Set 22ed 2024, p. 2030",
   "text": "Abdominal pain, vomiting, and diarrhea may also occur in children; in some studies, diarrhea was reported to be more often associated with influenza A(H1N1)pdm09 compared with influenza A(H3N2) or influenza B viruses. Influenza is a less distinct illness in younger children and infants. The infected young infant or child may be highly febrile and toxic in appearance, prompting a full diagnostic workup. The typical duration of the febrile illness is 2- 4 days. Cough may persist for longer periods, and evidence of small airway dysfunction is often found weeks later. Owing to the high transmissibility of influenza, other family members or close contacts of an infected person often experience a similar illness. ## **COMPLICATIONS**"
  },
  {
   "source": "Fever without a source in children 3 to 36 months of age: Evaluation and management - UpToDate, p. 2",
   "text": "- **Seasonal influenza** \u2013 Influenza occurs in distinct outbreaks every year, mainly during the winter months in temperate climates, although the specific timing and duration of the influenza season vary from country to country and year to year. Clinical features of uncomplicated influenza in children consist of fever, cough, and rhinitis. For children <5 years of age and especially <2 years of age, confirmation by laboratory testing is recommended due to the high risk of complications. (See \"Seasonal influenza in children: Clinical features and diagnosis\" and \"Seasonal influenza in children: Management\".) - **COVID-19** \u2013 Infants >3 months of age and young children with COVID-19 frequently have fever, pharyngitis, nasal congestion, and cough. Vomiting and diarrhea have also been described. Testing is necessary to confirm infection, although there is geographic variability in the criteria for testing. (See \"COVID-19: Clinical manifestations and diagnosis in children\", section on 'Approach to diagnosis'.)"
  },
  {
   "source": "CURRENT Diagnosis and Treatment Pediatrics, Twenty-Fourth Edition, p. 1227",
   "text": "## \u00bb **Clinical Findings** Spread of influenza occurs by way of airborne respiratory secretions. The incubation period is 2\u20137 days. ## **A. Symptoms and Signs** Influenza infection in older children and adults produces a characteristic syndrome of sudden onset of high fever, severe myalgia, headache, and chills. These symptoms overshadow the associated coryza, pharyngitis, and cough. Usually absent are rash, marked conjunctivitis, adenopathy, exudative pharyngitis, and dehydrating enteritis. Fever, diarrhea, vomiting, and abdominal pain are common in young children. Infants may develop a sepsis-like illness and apnea. Chest examination is usually unremarkable. Less frequent clinical findings include croup (most severe with type A influenza), exacerbation of asthma, myositis (especially calf muscles), myocarditis, parotitis, encephalopathy (distinct from Reye"
  },
  {
   "source": "Red_Book_2021_2024_Report_of_the_Comm_z_library_sk,_1lib_sk,, p. 497",
   "text": "Humans of all ages may sporadically be infected with emerging influenza A viruses of swine or avian origin. Most notable among avian influenza viruses are A (H5N1), which emerged in 1997 in Hong Kong, and A (H7N9), first detected in 2013 in China, both of which have been associated with severe disease and high case-fatality rates. Since 2017, Asian (H7N9) is considered the influenza virus with the highest potential pandemic risk. Infection with a novel influenza A virus is a nationally notifiable disease and should be reported to the Centers for Disease Control and Prevention (CDC) through state health departments."
  },
  {
   "source": "Kliegman R. Nelson Textbook of Pediatrics 2-Volume Set 22ed 2024, p. 2029",
   "text": "Influenza also causes a substantial burden of disease in outpatient settings. It contributes to an estimated 600,000 to 2,500,000 outpatient medical visits annually in children younger than 5 years of age and has been identified in 10\u201325% of outpatient visits among all children with respiratory symptoms during influenza season. Influenza may also be underdiagnosed. Many who seek medical care for influenza do not have laboratory testing performed and do not receive a diagnosis of influenza. Every year, three or four influenza virus types or subtypes typically co- circulate, including influenza A(H3N2), influenza A(H1N1), and two types of B viruses. Although one subtype usually predominates in any given season, it is difficult to predict which will be predominant. Thus the influenza vaccine varies annually and contains three or four antigens representing the expected circulating types. ## **PATHOGENESIS**"
  },
  {
   "source": "Red Book Atlas of Pediatric Infectious Diseases, p. 348",
   "text": "## **ETIOLOGY** Influenza viruses are orthomyxoviruses of 3 genera or types (a, B, and C). annual epidemics are caused by influenza virus types a and B, and both influenza a and B virus antigens are included in seasonal influenza vaccines. Type C influenza viruses can cause sporadic mild influenzalike illness in children. Type C antigens are not included in influenza vaccines. Influenza a viruses are subclassified into subtypes based on their surface antigens, hemagglutinin (Ha) and neuraminidase (na). examples of these virus subtypes include H1n1 and H3n2 influenza a viruses. Specific antibodies to these various antigens, especially to Ha, are important determinants of immunity. a minor antigenic variation that leads to changes in the Ha or na surface proteins of influenza a or B viruses is termed _antigenic drift._ antigenic drift occurs continuously and results in new strains of influenza a and B viruses, resulting in seasonal epidemics."
  },
  {
   "source": "Cover, p. 3599",
   "text": "illness in children, and type C antigens are not included in influenza vaccines. Influenza infection is initiated by virus inoculation in the upper or lower airways. If present, virus-specific IgG and IgA antibodies against the surface antigens, particularly HA, may block the infection. Neuraminidase facilitates penetration through the sialyloligosaccharide-rich respiratory mucous layer for access to the epithelial cells and later is important for release of newly packaged viruses from cells. The viral HA allows viral attachment and later membrane fusion with respiratory epithelial cells. Upon infection and replication in the respiratory epithelium, virus is shed into respiratory secretions, and local spread ensues, with eventual desquamation. The entire airway from pharynx to alveoli may be involved. Diffuse pneumonia due to alveolar infection can be life threatening. Viral infection usually remains limited to the respiratory tract, although viremia has been described with specific strains and has been"
  },
  {
   "source": "Kliegman R. Nelson Textbook of Pediatrics 2-Volume Set 22ed 2024, p. 2028",
   "text": "## **ETIOLOGY** Influenza viruses are large, single- stranded RNA viruses belonging to the family Orthomyxoviridae, which includes three genera (or types): A, B, and C. Influenza A and B viruses are the primary human pathogens causing seasonal epidemics, whereas influenza virus type C is a sporadic cause of predominantly mild upper respiratory tract illness. Influenza A viruses are further divided into subtypes based on two surface proteins that project as spikes from the lipid envelope, the hemagglutinin (HA) and neuraminidase (NA) proteins (Fig. 305.1). Strain variants are identified by antigenic differences in their HA and NA and are designated by the geographic area from which they were originally isolated, isolate number, and year of isolation\u2014for example, influenza ![](/tmp/pdf-images/pdf-2028-05.png) ![](/tmp/pdf-images/pdf-2028-06.png) ![](/tmp/pdf-images/pdf-2028-07.png) ![](/tmp/pdf-images/pdf-2028-08.png) ![](/tmp/pdf-images/pdf-2028-09.png)"
  },
  {
   "source": "MedStudy Pediatrics Core 11th Edition 2024-2025, p. 800",
   "text": "Severe disease, including myocarditis and CNS disease/ encephalitis, can also occur. Most often the diagnosis is made clinically. However, with less typical presentations or when considering the diagno- sis out of flu season, diagnosis of influenza is confirmed by isolating the virus (rarely done), by an enzyme immu- noassay (EIA)-based antigen detection assay (e.g., rapid flu test) or, more commonly nowadays, by PCR. Treatment in Children The CDC and the AAP provide the following indications for treating influenza with antiviral medications: * Any child hospitalized with presumed influenza * Children with confirmed or suspected influenza who have severe, complicated, or progressive illness * Influenza infection of any severity in children at high risk for complications, regardless of influenza immunization status \u00ab Any otherwise healthy child with influenza infection for whom a decrease in duration of clinical symptoms is felt to be warranted by his or her provider (particu-"
  },
  {
   "source": "Kliegman R. Nelson Textbook of Pediatrics 2-Volume Set 22ed 2024, p. 2587",
   "text": "With the exceptions of diphtheria (see Chapter 233), bacterial tracheitis, and epiglottitis, most other acute infections of the upper airway are caused by viruses. The parainfluenza viruses (types 1, 2, and 3; see Chapter 306) account for approximately 75% of cases; other viruses associated with croup include influenza A and B, adenovirus, respiratory syncytial virus, COVID- 19, and measles. Influenza A is associated with severe laryngotracheobronchitis. _Mycoplasma pneumoniae_ has rarely been isolated from children with croup and causes mild disease (see Chapter 269). Most patients with croup are between the ages of 3 months and 5 years, with the peak in the second year of life. The incidence of croup is higher in males. It occurs most commonly in the late fall and winter but can occur throughout the year. Approximately 15% of patients have a strong family history of croup. Recurrences are frequent from 3 to 6 years of age and decrease with growth of the airway. Recurrent croup is defined as two or more"
  }
 ]
}