The resurgence of swine-origin influenza A (H1N1)

CLINICAL FEATURES OF THE CURRENT OUTBREAK

The current S-OIV epidemic in the United States is affecting mainly younger people: 60% of people affected have been 18 years of age or younger.^10,11 It is unclear if this is due to transmission patterns or to possible immunity in older patients. Efficient human-to-human transmission within the United States is occurring, since only 18% of patients had recently traveled to Mexico. School outbreaks accounted for 16% of cases so far.

Patients have symptoms similar to those of seasonal influenza, with few exceptions. The most frequently reported symptoms are cough, fever, fatigue, headache, sore throat, runny nose, chills, and muscle aches, all occurring in 80% or more of patients. Almost all patients fit the CDC definition for influenza-like illness, consisting of subjective fever plus cough or sore throat.

Nausea, abdominal pain, and diarrhea, which are not common symptoms of seasonal influenza, have been reported in approximately 50% of patients with S-OIV. The spectrum of illness ranges from self-limited to severe, with 2% of patients developing pneumonia and 9% requiring hospitalization.

Continued analysis of the case-fatality rate highlights that people ages 20 to 29 are disproportionately represented among the fatalities.

A PCR test has been developed

Since clinical findings identify patients with influenza-like illness but cannot confirm or exclude the diagnosis of influenza,¹² a specific diagnostic real-time reverse-transcriptase polymerase chain reaction (RT-PCR) test has been developed, and the CDC is currently distributing it to state health departments.

An interim case definition

An interim case definition for the purpose of epidemiologic investigation of cases of S-OIV infection includes acute fever (temperature ≥ 100°F, 37.8°C) and acute respiratory illness (rhinorrhea, sore throat, or cough), plus:

• For a confirmed case, S-OIV infection confirmed by RT-PCR or viral culture
• For a probable case, laboratory-confirmed influenza A, but negative for H1 and H3 by RT-PCR
• For a suspected case, onset of above illness within 7 days of close contact with a confirmed case of S-OIV infection; or travel within 7 days to a community within the United States or internationally where there are one or more confirmed cases of S-OIV infection; or residing in such a community.

In practice, is it seasonal flu or swine flu?

In clinical practice in United States, in the springtime, a person with influenza-like illness and microbiologically confirmed seasonal influenza B obviously would not raise any concern about the ongoing S-OIV epidemic. Sporadic cases of seasonal influenza A are still occurring, but these are the ones that create a diagnostic dilemma, since very few laboratories currently have the ability to differentiate between influenza A H1 and H3. Since S-OIV has been reported in almost all states in the United States, one can argue that most cases of influenza A currently being identified should be considered suspected S-OIV.

PREVENTIVE MEASURES

In response to this ongoing outbreak, the WHO raised its epidemic alert level from 4 to 5, one level shy of declaring a pandemic. Several measures have been implemented in an attempt to halt this outbreak, the most important of which is the rapid dissemination of information to health professionals,¹³ with the Internet playing a central role.¹⁴

The world is better prepared for a pandemic now than at any time in history. Seed virus for vaccine development has been provided to various governments and pharmaceutical manufacturers. Stockpiles of antiviral agents are being mobilized and distributed to various locations, and dispensing plans are being reviewed for potential execution. The US Food and Drug Administration (FDA) issued emergency-use authorizations for mass deployment of the strategic stockpile of oseltamivir (Tamiflu), including for children younger than 1 year, and of zanamivir (Relenza) for the treatment and prophylaxis of S-OIV infection. It also authorized the use of disposable N95 respiratory masks by the general public, as well as the RT-PCR diagnostic test.

General advice for healthy people in the community

• Maintain a distance of at least 1 meter from a person with influenza-like illness.
• Wear a mask while providing care for a person with influenza-like illness.
• Avoid touching your eyes, nose, or mouth, since these are potential portals of entry for the virus. This may be a difficult recommendation to follow, since it requires constant vigilance of a common human behavior.
• Wash your hands often with either soap and water or an alcohol-based hand rub for 20 to 30 seconds, particularly after touching your eyes, nose, or mouth or after contact with respiratory secretions from a person, including your child, with influenza-like illness.
• If possible, reduce the time spent in close contact with people with influenza-like illness and in crowded settings.
• If possible, open windows in your living space to improve airflow.

While the CDC has recommended avoiding nonessential travel to Mexico at the current time, the WHO is not recommending any travel restrictions, since the outbreak has already spread to many parts of the world and all continents.

There is no limitation on handling or consuming pork meat or other well-processed swine products.

Recommendations for school dismissal and social-distancing interventions are evolving. During the 1918 pandemic, nonpharmaceutical interventions were associated with a significant reduction in deaths,¹⁵ but it is unclear how much additional benefit these measures would add to effective immunization, antiviral treatment for patients, and chemoprophylaxis for their contacts.

General advice for people with influenza-like illness

• Stay home for 7 days after the onset of symptoms or 48 hours after symptoms resolve, whichever is longer.
• Maintain a distance of at least 1 meter from all people.
• Cover your mouth and nose with tissues when coughing or sneezing, and dispose of the tissues immediately after use.
• Avoid touching your eyes, nose, and mouth.
• Wash your hands often with either soap and water or an alcohol-based hand rub for 20 to 30 seconds, particularly after touching your eyes, nose, or mouth or after contact with your respiratory secretions during coughing or sneezing. Adding virucidal agents or antiseptics to hand-washing is not likely to have an incremental effect.¹⁶
• If possible, open windows in your living space to improve airflow.
• If possible, when you are in close contact with other people, wear a mask to help contain your respiratory secretions.

Masks

The designs and standards of masks vary from country to country. Masks have been shown to reduce the transmission of influenza in health care settings,¹⁶ but the benefit in the community has not been established. Advice on proper use of a mask:

• Cover your mouth and nose with the mask and tie it securely to minimize gaps.
• Avoid touching the mask while it is on your face.
• Wash your hands with soap and water or an alcohol-based hand rub for 20 to 30 seconds after removing the mask.
• If the mask becomes damp, replace it with a new one.
• Avoid reusing single-use masks, and dispose of them immediately after removing.