MediArticles

Swine Flu History

Influenza viruses are small RNA viruses that infect many mammals, including humans, birds, and swine. Before 2009, swine influenza predominately affected swine and was not transmitted often or easily to people. Even in the isolated instances in which swine influenza infected people, it had very limited ability to spread from person to person. Most cases were directly linked to contact with swine through farming or at fairs.

Swine were first noticed to have influenza-like illnesses in 1918 during the human influenza pandemic. The term “pandemic” means that an infection has spread to many countries around the world, causing widespread human disease. Swine influenza did not cause the 1918 pandemic. Rather, pigs apparently acquired the infection from humans or from an undiscovered source. For decades, the swine virus remained relatively unchanged. In the 1990s, however, swine influenza viruses became more diverse and new strains appeared. The reason for this change is not clear but may have been related to overcrowding on large swine farms.

Before 2009, there was only one swine influenza outbreak in people that caused public-health concerns. This outbreak occurred in 1979, in soldiers at Fort Dix, New Jersey. One recruit died, and approximately 12 were hospitalized with influenza. Further testing showed that more than 200 recruits had acquired the virus, although most had few or no symptoms. The infecting strain was found to be strongly related to swine influenza virus, raising concerns that a new pandemic might occur. In response, public-health officials began a massive public vaccination program. Up to 25% of people in the United States were vaccinated. Unfortunately, the 1979 vaccine was associated with a small increased risk of Guillain-Barré syndrome, a serious neurological condition, with the risk estimated to be one to nine excess cases per million doses. Importantly, the 1979 strain did not spread easily from person to person and there was no epidemic. Human cases outside of Fort Dix were uncommon. Moreover, the 1979 vaccine was made using an old-fashioned process which is no longer utilized.

The lessons learned from the 1979 swine influenza event have been applied in dealing with pandemic threats, including the severe acute respiratory syndrome (SARS) outbreak of 2003 and the 2009 influenza outbreak. Key lessons include ensuring adequate communication with the public, producing a rapid but measured response to potential threats, and ensuring that any new strain fulfills criteria to cause a pandemic before large-scale vaccination is undertaken.

The 2009 outbreak of swine influenza (novel H1N1)

In March and April 2009, hundreds of cases of human respiratory illness were reported in Mexico that were suspected or confirmed to be caused by a novel swine-type influenza virus. By April, confirmed cases were also reported in the United States. The first reported cases in the U.S. came from San Diego County and Imperial County in California and Guadalupe County in Texas. Reports from other states rapidly followed, and the disease spread rapidly around the globe. The World Health Organization (WHO) has officially declared the 2009 swine flu to be a pandemic. The U.S. Centers for Disease Control and Prevention (CDC) estimates that more than 1 million Americans were infected with swine influenza by June 2009. By August 2009, more than 170 countries and territories reported swine flu cases. By October, 46 U.S. states were reporting widespread outbreaks. By late October, the virus had been confirmed to have caused more than 1,000 deaths in the U.S., with almost 100 of the deaths in children. Approximately 6% of deaths are in pregnant women, although only 1% of the population is pregnant. Physician visits, hospitalizations, and deaths in the fall of 2009 all exceeded seasonal thresholds. On Oct. 25, 2009, President Obama declared a national emergency as a result of the outbreak. This allows public-health officials additional power to allow waive some regulations to facilitate patient care and will allow hospitals to set up separate facilities to isolate sick patients.

Swine Flu Cause

Influenza viruses are named according to the types of proteins on the outer surface of the virus. The two main proteins are hemagglutinin (H) and neuraminidase (N). The swine influenza virus in the 2009 outbreak is an H1N1 virus. In fact, although the term swine flu is often used to describe the outbreak, the official term for the virus is novel H1N1 influenza.

It is important to realize that the influenza virus changes (mutates) constantly so that there are many strains of H1N1 that differ subtly from each other. Swine flu is caused by one strain of H1N1, but there are many other strains. Some H1N1 strains only infect pigs. Others infect humans, pigs, and birds. These subtle differences matter because the human body makes antibodies that are tailored to a single strain of influenza. If a person recovers from novel H1N1 (swine) flu, they are probably protected against infection from the same swine flu strain but are not protected against infections from variations on the strain or from other strains of influenza.

The 2009 novel H1N1 swine influenza strain appears to be a result of genetic “reassortment,” meaning that it contains pieces of influenza from many different sources. The 2009 virus includes genes that come from bird influenza viruses, swine influenza viruses, and human influenza viruses. This strain has not previously caused infections in humans or pigs. Thus, it is unlikely that humans will have preexisting immunity to this new strain

Swine Flu Transmission

Swine influenza (novel H1N1) spreads from person to person, either by inhaling the virus or touching surfaces contaminated with the virus, then touching the mouth or nose. Infected droplets are expelled into the air through coughing or sneezing.

Early information suggests that swine influenza is about as contagious as the usual human influenza. If one person in a household gets swine flu, anywhere from 8%-19% of household contacts will get infected. Reports from the southern hemisphere suggest that swine influenza is causing slightly more infections than would be normal for an influenza season.

Swine Flu Symptoms

Swine flu is a respiratory infection. The CDC recommends that swine influenza be considered in people who have fever and respiratory symptoms, especially cough or a sore throat. Ill people may also have fatigue, chills, headache, or body aches. Nausea, vomiting, or diarrhea has also occurred in people with swine flu. Very young children may not complain of fever or have a cough but rather have listlessness or shortness of breath as their main symptom.

Children and young adults (ages 0-24 years) have the highest rate of infection. Older adults (>65 years) are less likely to have infections, leading some to speculate that older individuals might have “partial immunity.” Partial immunity occurs when people make antibodies against one virus that have some effect on another virus. Thus, older people who were exposed to a similar virus may be partly protected against swine flu. The key words here are may and partly. There is no guarantee that an older person is protected, and if they do get infected, they are at risk for complications requiring hospitalization. One recent study showed that 33% of people over age 59 have antibodies that might help protect against novel H1N1. However, if older people do get infected, the disease may be more severe, as is true of most influenza infections.

Although the infection is usually mild, some people with swine flu have experienced serious respiratory illness, including pneumonia or respiratory failure leading to death. Pregnant women are at high risk for severe disease. Of concern, most deaths have occurred in adults under age 65, including people under age 25. This is the opposite of what happens in a normal influenza season when most deaths occur in the elderly.

People with chronic medical conditions are always at higher risk for complications from influenza and this is also true of swine flu. These chronic medical conditions include asthma, chronic lung disease, heart disease, diabetes, suppressed immune systems (including from chemotherapy), and kidney failure.

People with swine influenza are assumed to be contagious from one day before getting sick until at least 24 hours after symptoms resolve. Children and people with weak immune systems may be infectious for longer periods (for example, 10 days).

When to Seek Medical Care

People with fever and mild respiratory symptoms should call their physician for guidance. If you live in an area that is not currently reporting any cases of swine influenza, your physician may direct you to come into the clinic to be evaluated. If you live in an area where swine influenza is circulating already, your physician may decide to treat you over the phone. The CDC recommends this approach to minimize the number of sick people who go out into the community or into a clinic once cases have been confirmed.

People who are seriously ill should seek medical attention immediately through an emergency room or other setting. This includes people with shortness of breath, confusion, dizziness, or alterations in consciousness. Small children may not be able to describe their symptoms, and parents should look for signs of rapid breathing, bluish skin, or reduced level of responsiveness, which should prompt immediate medical attention.

Swine Flu Treatment

Laboratory testing has shown that the 2009 swine influenza strain is sensitive to two antiviral medicines that are used to treat human influenza. They are oseltamivir (Tamiflu) and zanamivir (Relenza). Oseltamivir is given in pill form. Zanamivir is an inhaled medication. Both medications require a prescription. A few drug-resistant strains have been reported, but most swine flu strains remain sensitive. Older drugs like amantadine (Symmetrel) are not effective.

The government has released some of its stockpile of Tamiflu, but the drug may be in short supply in local pharmacies. Not everyone with swine flu needs to be treated. However, the drug should be given to people who appear to have swine influenza if they have chronic medical conditions that put them at risk for complications (see above) or if they are unusually ill.

Self-Care at Home

People who are suspected of having novel H1N1 (swine) influenza should stay home from work and not go into the community, including attending school or going to work. The CDC recommends that people with influenza-like illness remain at home until at least 24 hours after they are free of fever.

Over-the-counter medicines like ibuprofen (Advil) or acetaminophen (Tylenol) may be used to reduce fever or aches. Aspirin or aspirin-containing products should not be given to children 18 years of age or younger, due to the risk of liver damage (Reye syndrome). Always follow the package directions for any over-the-counter cold or flu remedy.