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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 7 February 2010, worldwide more than 212 countries and overseas territories or communities have reported laboratory confirmed cases of pandemic influenza H1N1 2009, including at least 15292 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 information.

Situation update:

In the temperate zone of the northern hemisphere, overall pandemic influenza activity continued to decline in most countries. The most active areas of transmission continue to be in later peaking areas, particularly northern Africa, South Asia, and East Asia. Of note, Senegal became the third country within the past month (and fifth overall) to confirm first cases of pandemic H1N1 2009 in West Africa. There is insufficient evidence at this point to determine if this heralds the beginning of a period of more widespread transmission in West Africa, which heretofore may have been largely spared a significant period of communitywide pandemic influenza virus transmission.

In North Africa, pandemic influenza transmission persists but substantial declines in activity have been observed over the past month across the region. In Morocco, levels of ILI have returned to near baseline, and in Egypt, the number of confirmed cases has declined considerably.

In South and Southeast Asia, pandemic influenza virus continues to circulate widely across the region, however, overall activity continues to decrease or remain low in most places. In India, influenza transmission persist, particularly in western, and to a lesser extent, in northern India, however, overall the numbers of cases have declined substantially. In Thailand, overall activity remains low and unchanged since the previous reporting period, however, focal areas of increased ILI activity were reported in central and northern Thailand.

In East Asia, pandemic influenza transmission persists across the region; however, overall activity has declined substantially in most places. In China, pandemic and seasonal influenza viruses continue to co-circulate, however, over the last several weeks, seasonal influenza type B viruses have been predominant. In Japan, influenza activity continues to decrease towards seasonal baselines, including in Okinawa which is experiencing greater levels of influenza activity than in other parts of the country. In Republic of Korea (S. Korea), levels of ILI have decreased substantially to near baseline levels.

In Europe, although pandemic influenza virus continues to circulate widely, particularly across central, southern, and eastern Europe, the overall intensity of pandemic influenza activity has declined substantially from peaks of activity seen earlier during the winter transmission period. Among 15 countries testing more than 20 sentinel respiratory samples, the proportion of samples testing positive for influenza ranged from 0-14%. Recent slight increases in rates of ARI in Slovakia, Slovenia, and the Russian federation, do not appear to be associated with detections of influenza viruses and may be due to other circulating respiratory viruses.

In Sub-Saharan Africa, limited data suggest that pandemic influenza virus transmission may be geographically localized in most countries reporting surveillance data to WHO, and the overall intensity of activity may be low.

In the Americas, both in the tropical and northern temperate zones, overall pandemic influenza activity continued to decline or remain low in most places. In Central America and Caribbean, pandemic influenza virus transmission persists but overall activity remains low or unchanged in most places. A high intensity of respiratory diseases with increasing trend was reported in Guatemala, however, the increased activity does not appear to be associated with increased detections of influenza viruses and may be due to other circulating respiratory viruses.

In temperate regions of the southern hemisphere, sporadic cases of pandemic influenza continued to be reported without evidence of sustained community transmission. Pandemic influenza (H1N1) 2009 virus continues to be the predominant influenza virus circulating worldwide. In addition to the increasing proportion of seasonal influenza type B viruses recently detected in China, low levels of seasonal H3N2 and type B viruses are circulating in parts of Africa, East and Southeast Asia and are being detected only sporadically on other continents.

The Global Influenza Surveillance Network (GISN) continues monitoring the global circulation of influenza viruses, including pandemic, seasonal and other influenza viruses infecting, or with the potential to infect, humans including seasonal influenza. For more information on virological surveillance and antiviral resistance please see the weekly virology update (Virological surveillance data, below).

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