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[MEDSCAPE]: 季节性流感:更新及推荐意见
2017年01月19日 时讯速递, 进展交流 暂无评论

Seasonal Influenza: Current Updates and Critical Recommendations

Mark P. Brady, PA-C  |  January 4, 2017

The influenza virus (shown), source of one of the most common infectious diseases, is a highly contagious airborne virus that causes an acute febrile illness and results in variable degrees of systemic symptoms, ranging from mild fatigue to respiratory failure and death.[1] Brush up on your seasonal influenza knowledge now and be prepared for your patients this flu season.

The image demonstrates a colorized transmission electron micrograph of the H1N1 influenza virus; surface proteins are in black.

Image courtesy of Wikimedia Commons | National Institute of Allergy and Infectious Diseases.

Influenza-like illness is characterized by fever (temperature of 100°F [37.8°C] or greater) with cough and/or sore throat. Influenza occurs most commonly in the United States during the fall and winter, with activity typically being greatest between December and March.[2] Twenty-two states and the District of Columbia reported local influenza activity during the week ending December 10, 2016; 20 states reported sporadic activity; Guam, the US Virgin Islands, and seven states reported regional activity; and Puerto Rico reported widespread activity.[3]

Image courtesy of the Centers for Disease Control and Prevention (CDC).

As with other diseases, prevention of influenza is the most effective strategy. Each year in the United States, a vaccine that contains antigens from the strains most likely to cause infection during the winter flu season is produced;[4] these vaccines become effective 10-14 days after administration. The Advisory Committee on Immunization Practices (ACIP) recommends that all persons 6 months of age or older have a routine annual influenza vaccination unless they have specific contraindications.[5]

Image courtesy of the CDC | Doug Jordan, MA.

For the 2016-2017 season, the ACIP did not change their recommendations for vaccine dosing for children 6 months of age through 8 years. Children in this age group who are in their first season of vaccination require two doses of influenza vaccine to optimize response. The doses should be administered at least 4 weeks apart. In children aged 6 months through 8 years who have received two or more doses of trivalent or quadrivalent influenza vaccine before July 1, 2016, only one dose is required for the 2016-17 season. (It is not necessary for the child to have received the two prior doses during the same or consecutive seasons.)[5] The ACIP influenza vaccine dosing algorithm for children aged 6 months through 8 years is shown.

Image courtesy of the CDC.

The ACIP updated its recommendations for the use of live attenuated influenza vaccine (LAIV) and inactivated influenza vaccine (IIV) when either is available. In June 2014, the ACIP recommended that LAIV be preferred over IIV based on evidence of relative efficacy. However, data from subsequent observational studies indicated that LAIV did not perform as well as expected.

Due to its low effectiveness against influenza A(H1N1)pdm09 in the United States during the 2013–14 and 2015–16 seasons, the ACIP released an interim recommendation against the use of LAIV4 in the 2016–17 season.[5] The image demonstrates administration of an LAIV nasal spray.

Image courtesy of the CDC | Douglas Jordan, MA.

Although rare, severe allergic and anaphylactic reactions from influenza vaccine components can occur. For the 2016–17 influenza season, ACIP recommends that patients with a history of egg allergy who developed only hives after egg exposure can receive any age-appropriate IIV or trivalent recombinant influenza vaccine (RIV3).[5] Patients who report having had egg-associated reactions such as angioedema, respiratory distress, lightheadedness, or recurrent emesis or who required emergency medical intervention such as epinephrine administration may also receive any licensed and recommended influenza vaccine. For this latter group, however, vaccine administration should occur in settings containing personnel and equipment capable of rapid recognition and treatment of anaphylaxis.[6,7] Updated CDC guidelines no longer state that it is necessary to observe people with egg allergies for 30 minutes for an allergic reaction following a flu vaccination.[5] Influenza vaccination recommendations for persons with an egg allergy are shown.

Image courtesy of the CDC.

Four types of influenza viruses exist: A, B, C, and D. (Type D, which primarily affects cattle, has not been found in humans.) In the United States, nearly every winter, epidemics arise from human influenza A and B viruses.[8] Influenza A viruses are categorized into subtypes, with these divisions related to two proteins on the virus's surface, specifically hemagglutinin (H) and neuraminidase (N). These subtypes can themselves be divided into separate strains. In the 2015-16 flu season, influenza A viruses predominated nationally, accounting for about 70% of the isolated flu viruses.[9] The 2015-16 influenza season was less severe overall than were the previous three seasons.[9]

The above image demonstrates the hemagglutinin and neuraminidase surface proteins on an influenza virus particle, with a cross section revealing ribonucleoprotein (RNP).

Image courtesy of the CDC.

Influenza viruses spread from human to human via aerosols created by coughs or sneezes of infected individuals (shown). The incubation period of influenza ranges from 18-72 hours. Viral shedding occurs at the onset of symptoms or just before the onset of illness (0-24 h). Shedding continues for 5-10 days. Young children may shed virus longer, placing others at risk for contracting infection with the virus. Shedding may persist for weeks to months in highly immunocompromised persons.[1]

Image courtesy of the CDC | James Gathany.

The presentation of influenza virus infection varies; however, it usually includes many of the symptoms shown here. Patients with influenza who have preexisting immunity or who have received vaccine may have milder symptoms. Abrupt onset of illness is common. 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 (40°C). Sore throat can be severe and may last 3-5 days.

Image courtesy of Wikimedia Commons | Mikael Häggström.

This table shows the sensitivity and specificity of specific symptoms when diagnosing possible influenza.[10] Myalgias are common and range from mild to severe. Frontal/retro-orbital headache is also common and is usually severe. Ocular symptoms develop in some patients with influenza and include photophobia, burning sensations, and/or pain upon motion. Cough and other respiratory symptoms may be initially minimal but frequently progress as the infection evolves. In children, diarrhea may be a feature.[1]

Table data from Call SA, Vollenweider MA, Hornung CA, et al. JAMA. 2005 February 23;293(8):987-97. PMID: 15728170[10]

Influenza-positive tests reported to the CDC during the 2015-16 flu season are shown. Rapid influenza diagnostic tests can directly detect influenza A or B virus–associated antigens or enzyme in throat swabs, nasal swabs, or nasal washes and produce results in less than 30 minutes. However, because of cost, availability, and sensitivity issues, most physicians diagnose influenza based on clinical criteria alone. Findings of standard laboratory studies, such as a complete blood cell count and electrolyte levels, are nonspecific but helpful in the workup of influenza. Leukopenia and relative lymphopenia are typical findings in influenza. Thrombocytopenia may be present.[1]

Image courtesy of the CDC.

It can be difficult to accurately diagnose influenza A or B solely according to clinical criteria, owing to overlap from symptoms resulting from various viruses linked to upper respiratory tract infection (URTI) or from bacterial causes of pharyngitis.[11] Influenza-like symptoms can also arise from serious viruses such as adenoviruses, enteroviruses, and paramyxoviruses. In addition, influenza symptoms can be mimicked early in the presentation of mild or moderate flavivirus infections, such as dengue. Like influenza, URTIs from these viruses are more common in the winter. The seasonal variation of selected URTI pathogens is shown.

Image courtesy of Medscape.

Patients with influenza generally benefit from bed rest, and most patients recover in 3 days; however, malaise may persist for weeks.[1] After the development of influenza, antiviral agents can reduce the duration and severity of illness. To be effective, the medications must be administered within 40 hours of symptom onset. Oseltamivir is taken orally (75 mg bid for 5 d), and zanamivir is taken via an inhalation apparatus (10 mg bid for 5 d). A third antiviral drug, peramivir, is taken intravenously as a single 600 mg dose. All three are recommended by the CDC and ACIP to fight influenza. These agents work by inhibiting influenza virus neuraminidase, a glycoprotein spike that protrudes from the virus envelope; this spike is needed for successful cellular release of the virus and transmission within the body. Oseltamivir resistance has occurred during past influenza seasons. For example, during the 2007-08 influenza season, 10.9% of H1N1 viruses tested in the United States were resistant to oseltamivir.[12] For the 2015-16 season, most of the influenza viruses tested proved susceptible to the above three antiviral drugs, although again, a small number of H1N1 viruses were found to be resistant to oseltamivir.[13]

Image courtesy of Wikimedia Commons | Moriori.

Laboratory-confirmed influenza hospitalizations as of December 3, 2016, are shown. Most frequently, hospitalization is necessary when influenza exacerbates underlying chronic diseases. Some patients, especially elderly individuals, may be too weak to care for themselves alone at home. On occasion, the direct pathologic effects of influenza may require hospitalization; most commonly, this is influenza pneumonia.[1]

Image courtesy of the CDC.

This image shows bilateral interstitial infiltrates in a 31-year-old patient with influenza pneumonia.

Influenza pneumonia must be differentiated from other forms of viral pneumonia, bacterial pneumonia, and noninfectious causes of respiratory distress, such as congestive heart failure, chronic obstructive pulmonary disease, pulmonary edema, and aspiration pneumonitis.[1]

Image courtesy of Medscape.

This chest radiograph shows bilateral opacities with a predominantly peripheral distribution in a 48-year-old patient with Haemophilus influenzae pneumonia. In elderly or high-risk patients with pulmonary symptoms, chest radiography should be performed to exclude pneumonia.[1] Primary influenza pneumonia is characterized by progressive cough, dyspnea, and cyanosis following the initial presentation. 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.[1]

Image courtesy of Medscape.

Preparedness for pandemic influenza is widely considered to be grossly inadequate. The following five areas are important to managing a surge in severe illness: surveillance and diagnostic services, information sharing and dissemination, community support, hospital and physician capacity, and availability of vaccines and drugs.[1] Even in the absence of a pandemic illness, the lack of capacity in U.S. emergency departments has been described as a crisis by the Institute of Medicine.[1,14] For more information about preparedness for pandemic influenza, see the World Health Organization website.[15]

Image courtesy of Dreamstime | Photoroller.

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