December 2003

In preparation for the upcoming annual influenza season, the Advisory Committee on Immunization Practices (ACIP) recommends that the optimal time to receive influenza vaccine remains October through November.

Influenza immunization can be given at any month prior to or during an annual influenza epidemic. The seasonal epidemic is believed to begin in mid-winter, peaks within two to three weeks, and trails off after six weeks.

However, recent data from the United States has proved that the virus can be detected in the mid-Atlantic states as early as late November and as late as early March. Often there are two different influenza viruses circulating (influenza A and influenza B) in the same season. An attack of influenza A confers no immunity for influenza B, even in the same season.

Attack rates

The highest attack rate for influenza is among preschool and school-age children, who experience attack rates of 20%-30% or even higher in day care settings. The hospital admission rate of children younger than 2 years without underlying chronic diseases is similar to that of children 5 to 17 years of age with underlying cardiac, pulmonary, renal, endocrine or muscular conditions.

The incubation period for influenza viruses averages 48 hours, with a range of one to four days. The extent and duration of shedding of influenza virus from the nose and throat are more prominent in children. While adults shed influenza virus for only one day prior to the onset of clinical symptoms, young children can shed virus for up to six days prior to the onset of symptoms.

Serological surveys of individuals show that asymptomatic influenza (without any respiratory symptoms) accounts for about two-thirds of all influenza infections. Yet, these infected people can transmit the influenza virus through infected hands.

Children can be infectious for up to 10 days after the onset of symptoms. Respiratory illness caused by influenza is difficult to distinguish with certainty from illness caused by other respiratory viruses, especially at the onset and tail end of a seasonal epidemic. Most symptoms resolve after three to six days; however, cough, lethargy and malaise can persist for several weeks.

Complications

Complicated influenza is not rare in infants and toddlers, and the hospitalization rate in that age group is also similar to the rate of hospitalization in the group aged 50 to 64 years. Complications of influenza include influenza pneumonia, painful myositis (inflammation of muscles), encephalitis, myocarditis (inflammation of heart muscle) and Reye’s syndrome.

The highest attack rate for influenza is among preschool and school-age children, who experience attack rates of 20%-30% or even higher in day care settings. The hospital admission rate of children younger than 2 years without underlying chronic diseases is similar to that of children 5 to 17 years of age with underlying cardiac, pulmonary, renal, endocrine or muscular conditions.

Influenza vaccine is the primary method for the prevention of influenza disease. Vaccination has been proven to reduce hospital admissions, physician visits and influenza-related exacerbation of bronchial asthma. It also reduces person-to-person spread in day care centers, schools and households.

Compared with other respiratory viruses, influenza causes higher and longer fever and increased day care and school absenteeism. The numbers of medical visits or missed work days because of the need to care for ill children is higher with influenza than most other respiratory viruses for children of all age groups.

This year, sufficient supplies of live-attenuated or killed influenza vaccines are available. The 2003-2004 influenza vaccine includes A/Panama/2002/99-like (H3N2), A/New Caledonia (H1N1) and B/Hong Kong antigens.

The vaccine is estimated to be at least 80% effective in preventing influenza virus respiratory symptoms. Everyone wanting to receive a “flu shot” should be able to get one, if there are no contraindications. The AAP and the ACIP currently encourage the administration of killed influenza vaccination of all children 6 to 23 months old and next year the word “recommends” will replace the word “encourages.”

In our small pediatric office in Vienna, Va., we have tested several novel strategies to offer influenza vaccine to all eligible children, and even their parents, and receive fair payment for this service. Previously, our cost analysis of purchase and administration of killed influenza vaccine showed that we were losing considerable money when we billed third-party payers (medical insurance companies).

Some payers refused to reimburse us for any costs; some reimbursed us for the actual cost of vaccine, not including administration costs or the costs of record keeping, billing and injection of the vaccine. Other companies paid a fair amount for this service but we estimate that we lost between 30% to 40% of our true costs to purchase, store, administer and bill third-party payers.

Policy in my practice

In early October 2003, we instituted a policy that we will provide influenza vaccination, after on-site payment, to children or their parents, during regular office hours. We immunize during office visits, by special appointment and on selected “Flu Shot Saturdays.”

Our charge for the vaccine, including administration, is $20. The charge is about the same as that of major drug store chains in our area. While some other practices charge as much as $35 for administration of influenza vaccine, we elected to keep prices low to avoid complaints from patients to third-party payers.

We no longer bill third-party payers for influenza vaccine. Parents must sign a release form giving their consent to pay for the influenza vaccine on their own.

We actively encourage parents in our practice to immunize their children, beginning at the 6-month checkup. By starting in early October, the office staff has been able to keep up with the heavy demand for the vaccine. By the third week in October, we had given out more than 300 immunizations to office staff, pediatricians, parents and children. We plan to have several Saturday mornings for “flu vaccine clinics.” This year, for the first time ever, we are in the black for influenza vaccine.

Testing

Anti-influenza drugs must be started within 48 hours of the onset of symptoms of influenza to be effective. Rapid and timely detection of influenza virus can be best performed with an on-site test. There are several in-office, CLIA-waved rapid antigen tests for influenza. In addition to Directigen Flu A and B (Becton Dickinson) and Flu OIA (Biostar), QuickVue Influenza Test (Quidel) is now CLIA waived. These tests use a nasal wash or nasal swab specimen, a short extraction procedure similar to rapid streptococcal antigen tests, and use of a plastic-coated strip or plastic triangle-shaped detection device.

The Directigen test separates results for influenza A or influenza B, while the QuickVue test provides only the combined results for both influenza types. We have evaluated several tests in our office and compared the results to influenza culture. The tests are sensitive, specific and accurate for influenza A but not for influenza B. In recent years, influenza B has accounted for 25% to 30% of submitted respiratory specimens during influenza season. Influenza B has typically peaked about three or four weeks after influenza A has diminished in frequency.

We charge $20 for performance of a reliable on-site rapid antigen detection “flu test.” If the patient prefers, the child can be taken to a reference laboratory where the test can be performed free. However, since the results take two or three days to arrive at my desk, there is very little opportunity to help the child by prescribing specific anti-influenza medication. Since most of our patients are middle-class, very few opt for the reference laboratory to perform the rapid influenza test.

The advantages of on-site performance of the rapid test for influenza are reductions in unnecessary prescriptions for antibiotics and the ability to accurately diagnose influenza as a cause of the child’s fever, cough and malaise. Moreover, rapid, accurate diagnosis of influenza allows us to prescribe precisely appropriate therapy for influenza with amantadine, rimantadine or oseltamivir (Tamiflu, Roche). Specific anti-influenza therapy rapidly improves clinical symptoms, shortens the course of fever, myalgias and malaise and reduces communicability and time and money spent on office visits or unnecessary antibiotics.

For more information:

• Rodriguez WJ, Schwartz RH, Thorne MM. Evaluation of diagnostic tests for influenza in a pediatric office. Pediatr Inf Dis J. 2002; 21(3):193-196.
• Ruest A. Comparison of the Directigen flu A+B test, the QuickVue influenza test, and clinical case definition to viral culture and reverse transcription-PCR for rapid diagnosis of influenza virus infection. J Clin Microbiol. 2003; 41(8):3487-3493.
• Couch RB. Prevention and treatment of influenza. N Engl J Med. 2000:343(24):1778-1786.
• Meissner HC. Influenza: Emerging control of an old disease. Pediatr Emerg Care. 2001:17(6):465-470.
• Heikkinen T, guest editor: Influenza in Children: The unrecognized burden. Pediatr Infect Dis J. 2003;22 (Suppl. No. 10) S203-S235.