This is an excellent article from Ryan Maves, M.D. a doctor who works at the U.S. Naval Medical Research Center Detachment (NMRCD). I like to share this with our readers and bloggers
Familiarity breeds contempt. Every year, between 5-15% of the world’s population is infected with the influenza virus. These infections usually cause a typical upper respiratory illness, one of many lumped together as the “common cold,” but in a significant minority of cases, more severe disease and even death may result. Much of this illness occurs in the background; individual people may die of pneumonia, heart attacks, or some other common cause, but their sickness was the result of an initial influenza infection. The Centers for Disease Control and Prevention (CDC) in the United States estimates that some 36,000 people die in the US every year as the result of influenza. In Perú, the annual number of cases and deaths due to influenza are still being determined, but we can reasonably expect them to be at least proportional to those in the US. (Perú’s population of 29 million is a little less than 10% than that of the US.) With influenza such a common illness, we rarely pay it much attention, until something changes.
This year, something changed. Influenza viruses may change (or mutate) a small amount every year, an event we call antigenic drift. Unlike some commons viruses like chickenpox, where a prior infection leads to lifelong immunity, antigenic drift means that influenza is a little different every year. This prevents us from being significantly protected from this year’s virus, even though we were infected with last year’s virus. This is also the reason that people are offered a new influenza vaccine every year. Vaccine manufacturers, epidemiologists, and physicians make an educated guess about what a given year’s influenza strains will be. Those strains are then included in the new vaccine. Some years, the guess matches up well with the actual influenza strains circulating among humans. Some years, it doesn’t, and influenza spreads more rapidly.
Influenza is a zoonosis, an infection transmitted to humans from animals. Influenza viruses circulate freely among wild birds and mammals as well as their domesticated counterparts: ducks, chickens, pigs, and others. As viruses are transmitted between humans and animals, the genes of these different strains can “swap” between each other, leading to new and different types of influenza. This is called antigenic shift, and it leads to a more dramatic change in influenza that has the potential to spread very rapidly between people, with more cases and potentially more deaths.
Influenza, like all viruses, is made up of a number of different proteins. We use two particular proteins to categorize influenza viruses: hemagglutinin (H) and neuraminidase (N). The current H1N1 influenza virus appears to be related to a similar virus commonly found in pigs, hence the name “swine flu.” It seems that influenza viruses from bird and human strains mixed within groups of pigs, leading to this new virus. As of the 9th of July, 2009, 1,331 cases of H1N1 influenza have been identified in Perú, with three deaths. Three deaths are too many, but this is happening in the background of the normal Southern Hemisphere influenza season. We do not know how many additional total influenza cases are happening in Perú as a result of H1N1, although the Peruvian Ministry of Health and many partner organizations, including the Pan-American Health Organization (PAHO) and my institution, the U.S. Naval Medical Research Center Detachment (NMRCD), are working hard to determine this.
Compare this number of cases in Perú to the number in the United States. On the 10th of July, 2009, the CDC reported 37,246 confirmed cases and 211 confirmed deaths. However, the CDC estimates that the total number of cases may be as high as a million. Remember, also, that it is not the regular influenza season in the US; as in Perú, influenza in the Northern Hemisphere is a disease of late autumn and winter. Other countries cite similar figures: over 7,000 cases and 3 deaths in the United Kingdom, nearly 8,000 cases and 25 deaths in Canada, and 5,300 cases with 10 deaths in Australia (which is, admittedly, not in the Northern Hemisphere). Other populous nations in South America have reported higher rates of both cases and deaths, most notably Chile (7,300 cases and 14 deaths) and Argentina (2,500 cases and 60 deaths). These variable figures tell us something important about the limitations in our ability to study infectious diseases: the rates we report depend greatly on the groups we study. In Argentina, sicker patients are more likely to be tested for H1N1, so the number of deaths seems higher than elsewhere.
Another important issue is our choice of words when we describe disease outbreaks. In epidemiology, the word epidemic means a rate of disease higher than some predetermined “usual” rate. A pandemic happens when this higher epidemic rate of infection happens in multiple regions of the world. It is important to remember that epidemics and pandemics refer to the number of cases, not their severity. Unlike the highly-lethal H5N1 avian influenza found in eastern Asia and the Middle East (and which is not transmitted between humans except in extremely rare circumstances), the current H1N1 swine influenza is a relatively mild illness. Those few unfortunate deaths have happened mainly in people who would be at risk of death from normal seasonal influenza: the elderly, people with weakened immune systems, and people with heart or lung diseases.
So what does this all mean for us here in Perú? To put it simply, don’t panic. We can’t completely prevent its spread, but we can minimize it through simple measures: frequent handwashing, covering our mouths with the crook of our elbows when we cough, and staying home from work or school when we’re sick. For people who are exposed and at high risk from influenza, medications such as oseltamavir (TamiFlu) are still effective against H1N1, although there is still a risk that widespread resistance to these drugs could develop.
Different influenza strains may circulate in the Northern and Southern hemispheres. In some years, this means separate seasonal influenza vaccines for people who travel frequently between the hemispheres. A vaccine for H1N1 influenza is under development, and people at high risk of illness from infection (such as the elderly) or at high risk to transmit the infection (such as schoolchildren) should be strongly recommended to receive it. This vaccine will be in addition to the regular seasonal influenza vaccine. Again, people over 65 years of age, young children, pregnant women, and people with diseases of the heart, lungs, or immune system should all receive these vaccines assuming they are not allergic to some component of the vaccine (eggs, for example).
Oh, and just for the record: the inactivated flu shot cannot “give you the flu.” People may have some short-lived pain and even a low-grade fever after the injection, but this is brief and mild in the overwhelming majority of recipients. There is no living influenza virus in the usual vaccine1.
Influenza has always been with us, and this year’s H1N1 outbreak reminds us of the need to take this infection seriously. We could see a resurgence of the infection this winter in the Northern Hemisphere. Drug resistance to TamiFlu could complicate our ability to treat our most vulnerable neighbors. The infection could become more severe. These concerns are real. They are not, however, a cause for panic. H1N1 influenza is here in Perú, but for many of us, the number of cases is even higher in our home countries. There is no present reason for anyone from the US, Canada, Europe, or elsewhere to avoid travel South America because of influenza. Common sense, good hygiene, and vaccination are the best steps for all of us to keep ourselves and our families healthy in Perú.
The author would like to thank Dr. Alberto Laguna Torres, Dr. Tad Kochel, and Dr. Joel Sklar of NMRCD for their critical review of this article.
Dr. Maves is a graduate of the University of Washington School of Medicine in Seattle, Washington, and is board-certified in internal medicine and infectious diseases. He is an active-duty lieutenant commander in the U.S. Navy and presently serves as the head of the Department of Bacteriology at the U.S. Naval Medical Research Center in Callao, Perú. He is an assistant professor of medicine at the Uniformed Services University of Health Sciences in Bethesda, Maryland and lives in Lima with his wife, Robin, and their three children.
The views expressed in this article are those of the author and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, nor the U.S. Government.
Copyright statement: Ryan Maves is a U.S. military service member. This work was prepared as part of his official duties. Title 17 U.S.C. 1 105 provides that ‘Copyright protection under this title is not available for any work of the United States Government’. Title 17 U.S.C. 1 101 defines a U.S. Government work as a work prepared by a military service members or employees of the U.S. Government as part of those person’s official duties.