Influenza: Pediatricians should expect this influenza season to be a busy one

It is likely that both the seasonal influenza and the novel swine flu viruses will circulate this season. It is estimated that during the past season, there have been about 1 million cases of swine flu infection in the United States, which declined in the late spring.

During the past few months, the virus was widespread in parts of the Southern Hemisphere. The increase in cases in the southeastern United States in late summer may represent its expected return to the Northern Hemisphere. This virus appears to be contagious, having spread through schools and the population in general. Thus far, it does not appear to be unusually virulent given that our current experience is in an immunologically naive population, that is, no one has received vaccine. One cannot be certain, however, that it won't be more virulent as it returns this next season. This has happened in the past epidemics.

There have been approximately 50 deaths in children younger than 18 years and a significant number of these children had secondary bacterial infections. Ten of 23 for whom adequate specimens were available had superimposed bacterial infections, most commonly Staphylococcus and pneumococcus. It would be prudent to assure that children are up to date on their pneumococcal immunization.

One should consider the possibility of secondary bacterial infection in those whose condition appears to be deteriorating, have leukocytosis or are unusually severe. Antibacterial therapy should be reserved for these children. Others might benefit from antiviral therapy. Of the initial deaths reported in the pediatric age groups,"19% were aged younger than 5 years, and 67% had one or more high-risk medical conditions." Twenty-two of the 24 children with high-risk medical conditions had neurodevelopmental conditions. (MMWR. 2009;58(34):941-947).

The attack rate for the novel flu was highest in those aged younger than 2 years, with those children aged 2 to 4 years close behind. The hospitalization rate was particularly high in the youngest age group. Twenty percent of hospitalizations reported from California were in those aged younger than 5 years.

It is anticipated that vaccine against the novel influenza virus H1N1 will become available in October. Preliminary data indicate that one dose may be adequate for adults, which would mean that the vaccine supply could stretch further. In recognition of the severity of influenza in the very young, they have been prioritized for immunization. In addition, those likely to spread the disease to this vulnerable population are to receive the vaccine. Thus, initially the vaccine should be offered to children 6 to 24 months (this will be expanded to children up to 4 years of age when supplies are adequate), those caring for children younger than 6 months of age (parents, siblings and daycare providers) and pregnant women. It also is important to protect health care workers, including all those working in your offices, and those 25 to 64 years at increased risk for complications of influenza. It is likely that colleges will recommend immunization of students.

Rapid tests for influenza may be useful in situations where antiviral therapy is being considered. Nasal specimens are preferred. Compared with PCR, the specificity of rapid tests are good but the sensitivity poor. The sensitivity for the novel influenza is particularly poor. Thus, these tests never should be used to determine whether children could be returned to school. A negative test should not replace clinical judgment to determine whether a patient has influenza or not, according to CDC guidelines. (www.cdc.gov/h1n1flu/guidance/rapid_testing.htm). PCR may be available in some areas. Some laboratories became overwhelmed during the spring and limited the specimens they would accept. PCR is particularly useful during the start of an epidemic of influenza-like illness to determine whether the cause of illnesses are influenza virus and, if so, what type. This information will provide guidance as to the type of antiviral therapy recommended. Guidance on empiric treatment recommendations when multiple influenza strains are circulating is available at www2a.cdc.gov/HAN/ArchiveSys/ViewMsgV.asp?AlertNum=00279.

Although there have been rare reports of resistance of the novel influenza strain to oseltamivir, most are sensitive. They are resistant to the amantadines. It is recommended that those requiring hospitalization be treated and also those at high risk of complications, including those younger than 5 years and those with complications, including patients with neuromuscular disease that impairs respiration or clearing secretions, and patients with chronic lung disease, including asthma. To be effective, it is essential that treatment be initiated as soon after the onset of illness as possible. Prophylactic use is not recommended, except for those at high risk who have contact with a person with influenza (http://www.cdc.gov/h1n1flu/recommendations.htm).

It is likely that seasonal influenza will be circulating at the same time as the novel influenza. This has implications for the choice of antiviral therapy and for immunization. Although neuraminidase inhibitors are the drugs of choice for novel influenza, most seasonal influenza A isolates are resistant. Thus when both seasonal and novel A strains are circulating in the community, both drugs given simultaneously should be used in cases where antiviral therapy is indicated.

Novel flu vaccines

Both seasonal and novel swine flu vaccines will be required. Serologic evidence suggests that there will be virtually no protection against the novel flu from the seasonal vaccines. It is almost certain that two doses of the novel vaccine will be required for those younger than age 9. Those in this age group who have not been immunized with two doses of seasonal flu vaccine in the same year will require two additional seasonal influenza vaccine doses. One would be well advised to bring children in who require seasonal vaccine as soon as possible, especially those requiring two doses. Both killed vaccines can be given simultaneously, but if one uses live influenza vaccines, they should be separated by a one-month interval.

To reduce the risk of spread, children with respiratory symptoms and fever should not attend school. They can return one day after they are afebrile. If one family member is ill, students should stay home for five days from the day the illness develops. School closing is a much-debated issue. If a decision to close is made, children should stay home. Wandering through a shopping mall would be counterproductive.

The use of masks or respirators is of questionable value and is recommended under only special circumstances (http://www.cdc.gov/h1n1flu/masks.htm). It generally is not recommended for non-ill people, with the exception of some health care workers exposed to patients with the novel flu, but is recommended for ill patients in some circumstances to prevent spread.

At my granddaughter's school open house, we were assured that proper hygiene, including frequent hand washing or alcohol wipes, use and proper disposal of tissues and covering your nose when sneezing (with the antecubital area preferred to the hand) will be helpful.

For guidelines on antiviral therapy, use these recommendations issued by the Infectious Diseases Society of America: http://www.journals.uchicago.edu/doi/pdf/10.1086/598513?cookieSet=1.

For ongoing updates on the novel H1N1 outbreak, visit www.pediatricsupersite.com.