days of illness to be effective. They have been shown to reduce the disease course by 1 day. In addition, these agents prevent influenza illness in approximately 70 to 90% of individuals who take these agents prophylactically. Unfortunately, resistance to these drugs increased rapidly in influenza A H3 and 2009 H1N1. They do not work on influenza B. Therefore, in practice, these drugs are no longer used.
The second group of agents is the neuraminidase inhibitors. Two agents belong to this class of drugs—zanamivir, which is an inhaled agent, and oseltamivir, which is an oral agent. These agents are most effective if given in the first 2 days of illness and, like the ion channel-blocking agents, reduce the disease course by 1 day. However, data suggest that giving neuraminidase inhibitors at any time to a seriously ill patient may have benefits. The advantage of the neuraminidase inhibitors is that they are active against both influenza A and B viruses. However, influenza A H1 (pre-pandemic strain) is resistant to oseltamivir, and sporadic cases of H3 and 2009 H1N1 resistance have been described. To date, the majority of circulating influenza strains maintain susceptibility to both neuraminidase inhibitors.
7. Both vaccines are trivalent vaccines containing the same three influenza strains. The strains present in the 2012 vaccine included two subtypes of influenza A, 2009 H1N1 and H3N2, and influenza B. For the first time, in 2013 the vaccine contained two antigenically distinct influenza B viruses. It is important to remember that the composition of the vaccine changes annually. This is determined by the types of viruses that circulated during the previous season in the Southern Hemisphere. Due to waning immunity and antigenic drift of the viruses, the vaccine must be given annually. The efficacy of the vaccine is dependent on the level of change that may occur from year to year in the circulating virus, but it is generally 60 to 70% effective. One vaccine is an inactivated vaccine and can be administered intramuscularly (to those 6 months or older) or intradermally (to those 18 to 64 years old). There is also a high-dose inactivated vaccine that is given to people older than 65. The other vaccine is a live attenuated vaccine given intranasally to individuals aged 2 to 49 years. The live attenuated vaccine should not be given to pregnant women, immunocompromised individuals, or those caring for immunocompromised individuals.
The Centers for Disease Control and Prevention recommends that influenza vaccines be given to at-risk populations (see the answer to question 4 for a listing of at-risk populations). This includes children aged 6 months to 4 years, people 50 years and older, and health care personnel who could transmit the virus to at-risk patients. The vaccine is not recommended for children <6 months of age, a population that would most likely benefit from influenza virus vaccination. Numerous studies have proven the efficacy of this vaccine strategy. Recent studies also show that immunocompetent children benefit from vaccination through reduction in hospitalizations, doctor office visits, antibiotic use, serious secondary bacterial infections, and spread to at-risk family members.
REFERENCES
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CASE 11
A previously healthy 9-month-old infant presented in mid-February with a 2-day history of irritability, fever, and upper respiratory congestion. The mother reported that over the previous 24 hours the child had difficulty breathing with coughing and wheezing. The child’s medical history included a normal delivery after a 9-month gestation without complications. She was up to date on all immunizations. At age 6 weeks the child was placed in a day care center so that the mother could return to work. Several of the infants at the center had been ill recently with colds, and one infant required hospitalization because of severe breathing problems.
On examination the child appeared agitated and had a temperature of 38.6°C. She had both tachypnea (respiratory rate of 70 per minute) and tachycardia (pulse, 200 beats/min). The ears, eyes, and throat were normal except that the oral mucous membranes and tongue were dry. The nasal mucosa was boggy with clear discharge. The lungs revealed diffuse inspiratory and expiratory wheezes. Findings from the rest of the examination were normal.
A chest radiograph revealed hyperexpansion of the lungs but no infiltrates. Arterial blood gases revealed hypoxemia and respiratory alkalosis. The child was admitted to the hospital because of moderate respiratory distress. Supplemental oxygen and intravenous fluids were administered along with bronchodilators and systemic corticosteroids. A rapid molecular test performed on a nasopharyngeal swab provided the diagnosis.
1 1. This child presented with bronchiolitis, an acute viral lower respiratory tract illness generally occurring in the first 2 years of life. What viruses can cause this syndrome? What are the epidemiologic clues in this case that makes one of the viruses most likely?
2 2. Describe the epidemiology of the agent causing her infection.
3 3. What characteristics of this virus are important in determining how the virus spreads in the respiratory epithelium? How does the pathogenesis of the virus contribute to the wheezing that often accompanies this infection?
4 4. Describe the diagnostic strategies available for the detection of this agent. Why is it important to establish this diagnosis quickly?
5 5. What prevention strategies exist to avoid initial infection with this virus and to keep it from spreading within the hospital?
6 6. Is specific therapy available to treat this virus?
CASE 11 CASE DISCUSSION
1. The differential diagnosis for this patient’s bronchiolitis included respiratory viruses such as the parainfluenza viruses, adenovirus, influenza A and B viruses, coronavirus, rhinovirus, metapneumovirus, and respiratory syncytial virus (RSV). Mycoplasma pneumoniae or Bordetella pertussis also could have caused her illness. RSV causes ~70% of bronchiolitis cases in children <2 years of age, with more severe cases typically occurring in children <6 months of age and premature infants. In the day care setting, any of these agents could spread easily. However, the fact that another child had recently been hospitalized supports RSV or influenza as the most likely causes, as these viruses generally cause more severe disease. All of the potential viral causes circulate in the winter months, with RSV infections typically occurring between December and February. Increased RSV incidence often overlaps with both influenza and metapneumovirus, so those viruses cannot be excluded based on the time of the year the patient presented. To definitively diagnose this patient with RSV, a laboratory test must