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Swine Flu Medical Information

Updated Wednesday, April 29, 2009

Overview

A novel influenza virus has rapidly emerged as an important human pathogen that has led to sporadic outbreaks in several countries, including the United States. At this time, there are too many uncertainties in this rapidly changing situation to predict how significant the risk to human health posed by this virus will be. However, there is potential it could result in a severe epidemic, or even a pandemic. Coordinated response efforts are rapidly escalating to prepare for such a possibility and include an international elevation of the pandemic alert level, federal recommendations to avoid non-essential travel to Mexico, partial deployment of antiviral stockpiles and CDC-issued interim guidance on many issues.

Case Counts (as of 4/27/09)

New cases are rapidly being identified in the U.S. and internationally. Daily updates can be found at www.pandemicflu.gov.

Virus

The swine flu virus is a unique triple reassortment virus primarily of swine (N. American and Eurasian) origin, but also with genetic elements of N. American avian and human viruses. It has not been seen before as a cause of human or swine infections.

Clinical Features of Human Swine Flu

U.S. cases have been generally mild with only one confirmed hospitalization, and no deaths. The affected age range has been 7-54 years and an early estimate on the secondary attack rate is approximately 20%. There are no cases with known exposure to pigs. Symptoms of U.S. swine flu cases have been similar to seasonal influenza, which is characterized by fever and respiratory symptoms such as sore throat, cough, or runny nose. Muscle aches and headache are common. Some have also had gastrointestinal symptoms such as nausea and vomiting, but data are incomplete to conclude this is a prominent feature of human swine flu infection. One of the greatest areas of uncertainty is the discordant observation of severity in cases detected in the U.S. versus Mexico. The true case fatality rate is unknown. Community mitigation efforts will be based on the pandemic severity index, which is determined by the case fatality rate. The incubation period is thought to be 1-7 days.

Transmission

Person to person and fomite (i.e. contamination of inanimate objects with respiratory secretions) spread are assumed to be the only transmission modes at this time. If gastrointestinal symptoms are prominent, stool may be infectious, but this is currently unknown. Swine flu cannot be acquired through consumption of properly cooked/cured pork products.

Vaccine

The existing seasonal flu vaccines are ineffective. New vaccine seed lots are being created for potential large scale development of vaccines. It is anticipated that no specific vaccine will be available for at least 4-6 months.

Antivirals

The isolates have all been susceptible to the neuraminidase inhibitors oseltamivir (Tamiflu) and zanamivir (Relenza) but resistant to the adamantanes (rimantadine and amantadine). Current guidelines for management (http://www.cdc.gov/swineflu/recommendations.htm) recommend neuraminidase inhibitors for confirmed cases. In communities where seasonal H1N1 is still circulating, suspected cases where seasonal H1N1 has not been ruled out should be treated with zanamivir or oseltamivir PLUS rimantadine (or amantadine) because of high level resistance to oseltamivir in seasonal H1N1 isolates.

Antiviral Prophylaxis

Instances where prophylaxis with a neuraminidase inhibitor can be considered include high-risk (i.e. medical complications, immunocompromised, etc.) contacts of confirmed/suspected cases, and healthcare workers who have had unprotected close contact with confirmed cases.

Community Mitigation

The presence of a single confirmed case within a state should prompt initiation of some community mitigation efforts within affected communities. Interim guidance is at http://www.cdc.gov/swineflu/mitigation.htm. Guidance is likely to change when the case fatality rate of human swine flu infections is better understood. Current recommendations are to institute home isolation of cases, close affected schools (K-12) and consider closure of other schools in a community with confirmed cases, and cancelling public gatherings at institutions where confirmed cases have been identified. Guidance on the use of masks in public settings is limited by lack of data on how effective this measure is. Interim guidance is located at http://www.cdc.gov/swineflu/masks.htm. Surgical mask or N95 respirator use can be considered for people who must be in crowded public spaces in communities where confirmed cases have been identified.