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Infectious

Influenza

An outbreak caused by a novel strain of H1N1 influenza, commonly called "swine flu", began in Mexico in March 2009 and spread rapidly to many other countries. The virus contains a unique combination of swine, avian, and human influenza gene segments that had not been previously observed. Initial reports from Mexico indicated a high fatality rate in previously healthy young adults and older children, raising concerns that a worldwide pandemic might occur, similar to 1918. However, subsequent data from Mexico, as well as experience from other countries, indicated the H1N1 strain from 2009 is not nearly as lethal as some people initially feared. Preliminary data indicate that up to one-third of those greater than 60 years of age have antibodies against the novel H1N1 virus, whereas protective antibodies are found much less frequently in children and younger adults (see MMWR). This is consistent with the clinical experience so far, which indicates that the most severe cases are occurring in those younger than age 60.

The World Health Organization does not recommend any travel restrictions at this time. To protect yourself from H1N1 influenza, wash your hands regularly and avoid close contact with anyone who is coughing or sneezing. Routine use of face masks is not recommended. The symptoms of H1N1 influenza include fever, cough, sore throat, body aches, headache, chills and fatigue, similar to seasonal influenza. Any traveler who develops flu-like symptoms after travel to a country which has reported H1N1 influenza should immediately seek medical attention. Empiric treatment with oseltamivir (Tamiflu) and zanamivir (Relenza) should be considered for suspected cases. A small number of Tamiflu-resistant isolates have been described, but these strains have retained sensitivity to Relenza. The virus is uniformly resistant to amantadine and rimantadine. Vaccination against novel H1N1 influenza is recommended for everyone, except those allergic to the vaccine or one of its components. For further information on novel H1N1 influenza (swine flu), go to the World Health Organization and the Centers for Disease Control.

The following is the latest update from the World Health Organization:

As of 27 December 2009, worldwide more than 208 countries and overseas territories or communities have reported laboratory confirmed cases of pandemic influenza H1N1 2009, including at least 12220 deaths.

WHO is actively monitoring the progress of the pandemic through frequent consultations with the WHO Regional Offices and member states and through monitoring of multiple sources of data.

Situation update:

The most active areas of pandemic influenza transmission currently are in central and eastern Europe. Focal increases in rates of ILI/ARI during recent weeks were reported in at least three eastern European countries, Georgia, Montenegro, and Ukraine. A high intensity of respiratory diseases activity with concurrent circulation of pandemic influenza persists in parts of southern and eastern Europe, particularly in Greece, Poland, Bulgaria, Serbia, Ukraine, and the Urals Region of the Russian Federation. In Western Europe, influenza transmission remains active and widespread, but overall disease activity has peaked. At least 13 of 21 countries (testing more than 20 sentinel samples) reported that 30% or more of sentinel specimens were positive for influenza, down from a peak of over 70%. All were influenza viruses detected in Western Europe were pandemic H1N1 2009, however, very small numbers of seasonal influenza viruses, making up less than 1% of all influenza viruses detected, were reported in Russia. In addition, limited available data indicates that active, high intensity transmission is occurring in Northern African countries along the Mediterranean coast (Algeria, Tunisia, and Egypt).

In Central Asia, limited data suggest that influenza virus circulation remains active, but transmission may have recently peaked in some places. In West Asia, Israel, Iran, Iraq, Oman, and Afghanistan also appear to have passed their peak period of transmission within the past month, though both areas continue to have some active transmission and levels of respiratory disease activity have not yet returned to baseline levels.

In East Asia, influenza transmission remains active but appears to be declining overall. Influenza/ILI activity continued to decline in Japan, in northern and southern China, Chinese Taipei, and Hong Kong SAR (China). Slight increases in ILI were reported in Mongolia after weeks of declining activity following a large peak of activity over one month ago. In southern Asia, influenza activity continues to be intense, particularly in northern India, Nepal, and, Sri Lanka. Seasonal influenza A (H3N2) viruses are still being detected in very small numbers in China making up about 2.5% of the influenza A viruses detected there.

In North America, influenza transmission remains widespread but has declined substantially in all countries. In the US, sentinel outpatient ILI activity has returned to the seasonal baseline, and indicators of severity, including hospitalizations, paediatric mortality, and P and I mortality have declined substantially since peaking during late October. Rates of hospitalization among cases aged 5-17 years and 18-49 year far exceeded rates observed during recent influenza seasons, while rates of hospitalizations among cases aged less than 65 years were far lower than those observed during recent influenza seasons.

In the tropical regions of Central and South America and the Caribbean, influenza transmission remains geographically widespread but overall disease activity has been declining or remains unchanged in most parts, except for focal increases in respiratory disease activity in a few countries.

In the temperate regions of the southern hemisphere, sporadic cases of pandemic influenza continued to be reported without evidence of sustained community transmission...

Influenza background information:

Influenza is a viral infection characterized by fever, chills, malaise, headaches, body aches, and cough, sometimes complicated by pneumonia, which may be life-threatening. All age groups may be affected, but severe illness is more common in the elderly and in those with chronic illnesses such as asthma, diabetes, kidney failure, and heart disease. Influenza occurs in annual epidemics from November to March in the temperate regions of the Northern Hemisphere and from April to September in the temperate regions of the Southern Hemisphere. However, travelers in large groups, especially those on cruise ships, may be at risk year-round, due to exposure to influenza viruses carried by persons from other parts of the world. Influenza is reported sporadically throughout the year in the tropics.

Because influenza may cause significant distress during foreign travel, because medical care may be difficult to obtain while abroad, and because the symptoms of influenza, which are non-specific, may be confused with those of other illnesses, influenza vaccine should be seriously considered for all international travelers at risk, i.e. those traveling to the Northern Hemisphere between November and March, those traveling to the Southern Hemisphere between April and September, and those traveling on cruise ships or to the tropics at any time. Influenza vaccine is strongly recommended for all those over age 50 and for those with chronic medical conditions such as diabetes, emphysema, asthma, or heart disease. The vaccine should be given at least two weeks before departure.

Twice each year, before influenza season in the Northern and Southern Hemispheres, the World Health Organization makes recommendations for vaccine composition, depending upon which strains appear most likely to cause outbreaks. If influenza vaccine for the Southern Hemisphere is not available, the vaccine for the preceding influenza season in the Northern Hemisphere, if obtainable, is the recommended alternative. For the year 2009, the vaccine recommended for the Southern Hemisphere is the same as that which had been given in the Northern Hemisphere for the winter of 2008-2009.

The most frequent side-effect of influenza vaccine is mild discomfort at the injection site. Fever, malaise, and body aches may occur, but are typically mild. Severe reactions, generally allergic, are rare. Because the viruses in the vaccine are inactivated, influenza vaccine cannot cause influenza. Influenza vaccine should not be given to anyone allergic to eggs or in the first trimester of pregnancy.

A new nasal-spray flu vaccine was licensed in the United States in 2003. Unlike the injectable flu vaccine, it contains live, weakened flu virus. It includes the same strains of influenza as the injectable vaccine and appears to have comparable efficacy. In the United States, the nasal-spray vaccine is only approved for use in healthy people between the ages of 5 and 49.

The first-line drugs to treat influenza have been oseltamivir (Tamiflu) and zanamivir (Relenza) (PDF). However, in December 2008, the Centers for Disease Control reported that almost all the strains of influenza A (H1N1) isolated to date that winter were resistant to oseltamivir (Tamiflu). In March 2009, the World Health Organization reported high prevalence of oseltamivir resistance among H1N1 strains from Canada, Hong Kong SAR, Japan, the Republic of Korea, the United States, France, Germany, Ireland, Italy, Sweden and the United Kingdom. The CDC has therefore advised that, when influenza A (H1N1) virus infection or exposure is suspected, zanamivir or a combination of oseltamivir and rimantadine (Flumadine) should be given, rather than oseltamivir alone (see the Centers for Disease Control. Oseltamivir is available as 75-mg capsules, given twice daily by mouth for five days. The most common side-effects are nausea and vomiting, which are generally mild. Zanamivir is a dry powder prepared as an oral inhaler, given two inhalations twice daily for five days. Zanamivir may cause an exacerbation of asthma or chronic obstructive lung disease; it should be given with caution to persons suffering from those diseases. The usual dosage of rimantadine is 100 mg twice daily. Rimantadine should be avoided in those with a history of seizures, though the risk appears small. If rimantadine is not available, an older drug called amantadine is an acceptable alternative. Rimantadine and amantadine are only effective against influenza A viruses, as opposed to oseltamivir and zanamivir, which have been active against both influenza A and B.

From the World Health Organization

FluNet (Global Influenza Surveillance Network)

Influenza fact sheet

Influenza vaccine

Influenza vaccines - WHO position paper (PDF)

Influenza vaccine manufacturers

Influenza in the world 1 October 2000 - 30 September 2001 (PDF)

From the Centers for Disease Control (CDC)

Influenza Home Page

Influenza

Influenza: The Disease

Influenza: Prevention and Control