INFLUENZA - PROPHYLAXIS

Question:
Do the contacts need to take oseltamivir?

Answer:
This is a situation where the index case has influenza and he has been in contact with his brother and mother who is pregnant. Since the child has influenza A, he could be suffering from either seasonal influenza or H1N1. The question is whether the contacts have to be given chemoprophylaxis.

A patient with influenza remains infectious one day before fever begins until 24 hours after fever ends. As per CDC, the following persons who are a close contact of a person with suspected or confirmed influenza during the infectious period (a) Persons at high risk for complications of influenza; (b) Health care workers and emergency medical personnel; (c) Pregnant women should receive chemoprophylaxis. (1).

The following should not be given chemoprophylaxis: (a) Groups of healthy children or adults based on potential exposures in the community, workplace, school, camp or other settings; (b) If >48 hours have elapsed since the last close contact (c) The close contact did not occur during the infectious period.

Four licensed influenza antiviral agents are available: amantadine, rimantadine, zanamivir, and oseltamivir. However the neuraminidase inhibitors, oseltamivir and zanamivir, are the drugs of choice for chemoprophylaxis of influenza-exposed children and adults (1) Both, inhaled zanamivir and oral oseltamivir, are effective for treatment and prophylaxis of influenza A and B infection.

Table 1. Antiviral medication dosing recommendations for chemoprophylaxis of influenza infection.
(Table extracted from IDSA guidelines for seasonal influenza.)

Agent, group		Chemoprophylaxis
Oseltamivir
Adults		75-mg capsule once per day
Children >12 months	15 kg or less	30 mg once per day
	16-23 kg	45 mg once per day
	24-40 kg	60 mg once per day
	>40 kg	75 mg once per day
Zanamivir
Adults		Two 5-mg inhalations (10 mg total) once per day
Children		Two 5-mg inhalations (10 mg total) once per  day (age, 5 years or older)

Regarding pregnant women, CDC recommends post-exposure antiviral chemoprophylaxis can be considered for pregnant women and women who are up to 2 weeks postpartum (including following pregnancy loss) who have had close contact with someone likely to have been infectious with influenza. Close contact is defined as having cared for or lived with a person who has confirmed, probable, or suspected influenza, or having been in a setting where there was a high likelihood of contact with respiratory droplets and/or body fluids of such a person. (2) Zanamivir may be the preferable antiviral for chemoprophylaxis of pregnant women because of its limited systemic absorption. However, respiratory complications that may be associated with zanamivir because of its inhaled route of administration need to be considered, especially in women at risk for respiratory problems. For these women, oseltamivir is a reasonable alternative. The duration of antiviral chemoprophylaxis post-exposure is 10 days after the last known exposure. (2)

Thus, here both the mother and brother will need prophylaxis with antivirals as suggested above. As per CDC, most effective strategy for preventing influenza is annual vaccination.

References:

	1.	Center for Disease Control. Updated Interim Recommendations for the Use of Antiviral Medications in the Treatment and Prevention of Influenza for the 2009-2010 Season. Available at URL: http://www.cdc.gov/h1n1flu/recommendations.htm. Accessed on 17th September 2010
	2.	Center for Diseases Control. Updated Interim Recommendations for Obstetric Health Care Providers Related to Use of Antiviral Medications in the Treatment and Prevention of Influenza for the 2009-2010 Season. Available at URL: http://www.cdc.gov/H1N1flu/pregnancy/antiviral_messages.htm. Accessed on 17th September 2010