Influenza A (H1N1), the last pandemic

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Influenza A (H1N1), the last pandemic

Dr. Hugo Eduardo Pezzarossi Zelaya
Specialized in Internal Medicine and Infectious Diseases
Director of Prevent (Medical Prevention Services S.A.)

During the month of March, 2009, cases of influenza started being reported, in Veracruz, Mexico, as well as in Southern California. Weeks later it was possible to establish that it was a variant of the Influenza A virus, the subtype H1N1. Three months later, this emerging infection affected the population of 138 countries in the 5 continents and on June 11th, the WHO (World Health Organization) decided to elevate this pandemic to alert level 6, which does not define the severity of the disease produced by the virus, but its geographic extension.

By the time you read this document, it is absolutely certain, that the number of people affected by the last pandemic of the modern world will have infected several thousand more people. Up until, July 1st 2009, the WHO established 138 countries affected by the pandemic, which together officially report 29,669 cases of infection by Influenza A (H1N1) (1669 cases in Central America and Panama, 264 in Guatemala), figure that includes 332 related deaths, 2 in Guatemala, 2 in Costa Rica and 1 in Honduras. If it is true that this virus has shown a low lethality rate, its future behavior is still to be established.

Even though these data are official (source: WHO), they should in no way be considered real, considering a sub-register, particularly obvious in developing countries like ours, where we have been able to observe personnel poorly trained to provide timely and adequate attention to people with respiratory infections, absence of means to diagnose Influenza A (H1N1) and lack of control of sick people, among other difficulties, the Public Health authorities have had to deal locally with this pandemic.

TERM DEFINITION: For better comprehension of this document, I consider appropriate to define 3 terms:

  1. Virus (from the Latin, virus, which means toxin or venom), which is a biological entity that needs a host cell to replicate in, in the case of Influenza A (H1N1) the virus needs human cells to reproduce and cause sickness, using of course, its genetic material.
  2. Pandemic (from the Greek pandêmon nosêma, παν (pan = all) + δήμος (demos = people) + nosêma (disease), expression that means disease of all the people. It is an infectious disease that affects or compromises more people and in a more extended geographical area. To be specific, a pandemic is a global disease, and in the case of influenza, it happens when a new virus emerges among people that possess very little or no immunity (defenses) and for which there is no vaccine. Under these circumstances, the disease spreads easily with contact from person to person, and can extend within a city or around the world in a very short time. A pandemic by the Influenza virus can be caused by virus from pigs or birds.
  3. Influenza can be defined as a viral infection that compromises primarily the respiratory system (nose, throat, bronchia, and occasionally the lungs). In the absence of complications it tends to last a week and is characterized by high fever, muscle pain, headache and intense discomfort, dry cough, sore throat and rhinitis.

THE VIRUS: The influenza virus, isolated for the first time in 1933, is classified in the Orthomyxoviridae Family, belongs to Group V and groups Influenza genres A, B and C, and other viruses (lsavirus and Thogotovirus). While the Influenza A virus can infect birds and humans, horses, pigs, minks, seals and whales, the Influenza B virus only affects humans, and the Influenza C virus, humans as well as pigs.

In its structure, the influenza virus has 2 proteins present on its surface, denominated hemagglutinin (H) and neuraminidase (N). The subtypes of the Influenza A virus found now in human beings are A (H1N1) and A (H3N2), being Influenza A (H1N1), the virus responsible for the disease with characteristics of epidemic outbreak, that began in North America and at this time has already spread to the 5 continents.

THE PANDEMIC We must recognize that nowadays various types of Influenza circulate, being the 2 most important:

  1. Seasonal Influenza, preventable at a high percentage with adequate vaccination outlines.
  2. Pandemic influenza or pandemic of virus Influenza A (H1N1), purpose of this document. While seasonal Influenza occurs during the whole year, generally during the winter months, the new pandemic just made its presentation and everything is left to find out about its future behavior.

When a new disease or pandemic emerges, the WHO, to make comprehension easier, increases its precision and bases it on observable phenomena and structures phases. Phases 1 to 3 are related to preparation, in which capacity development activities and response planning are included, while phases 4 to 6 clearly point at the need of response measures and mitigation. The pandemic we are referring to is found in phase 5, that is, a phase characterized by the spread of the virus from person to person at least in two countries of a WHO region. Even though most countries will not be affected in this phase, the declaration of phase 5 is a clear indication of the imminence of a pandemic and that there is little time to organize, communicate and put in practice the planned mitigation measures. Phase 6, as to say the pandemic phase, is characterized by the criteria that define phase 5, accompanied by community outbreaks in at least a third country of a different region. The declaration of this phase indicates a world pandemic is happening.

A post-peak period is also described, in which the levels of the pandemic, in the countries that observe adequate vigilance, will decrease to levels inferior to those observed during the highest peak, which means the activity of the pandemic is decreasing. However, it is predictable if recurrent events, new outbreaks or waves, occur, and countries need to be prepared for such eventuality. The accumulated experience supports that pandemic waves can be separated by months, not as to allow “lowering the guard”, but it forces the health authorities to keep the state of alert.

HISTORY: Although certain accumulated scientific evidence has allowed us to know of a pandemic caused by Influenza A, subtype H2N8, in 1889-90, and of an epidemic of A (H3N8) in 1900-03, it was not until 1918 that the so-called Spanish Flu occurred. An intense pandemic caused by A (H1N1) that was responsible for 50-100 million deaths and in which the index case (first case) happened in March of 1918, in Fort Riley, Kansas, United States.

Since then, there have been mild epidemics (1933-35) caused by A (H1N1), as well as mild to intense pandemics, that took place in 1957-8 by A (H2N2) (Asian Flu initiated in Beijing, moderate), in 1968-9 by A (H3N2) (Hong Kong, intense), in 1977-8 by A (H1N1) (Russian Flu, mild) and in 2009 by A (H1N1) (North American Flu, magnitude to be established).

Outbreaks of swine flu A (H1N1) have happened in 1976, bird flu (H5N1) in 1997 (Hong Kong), with sporadic cases in humans that year and in the 2000s, without making it to the category of an epidemic, but forcing the WHO to keep level of alert 3 until this year.

Records exist of swine flu that affected humans. In 1988, a presumed outbreak in pigs in Wisconsin caused multiple infections in human beings, and, even though there was not an outbreak in the community, antibodies were identified that proved the transmission of the virus from a patient to the health personnel with which he had been in close contact.

In 1976, an outbreak of swine flu among the soldiers of Fort Dix, New Jersey, United States, caused pneumonia in at least 4 previously healthy soldiers and one of them died. Later, the virus was transmitted to nearby contacts in a basic training zone, with no extension outside this group, and with no posterior knowledge of related cases. This outbreak could have been caused by the transmission of the swine influenza type A virus, to a soldier of Fort Dix. Finally, this virus was baptized as A/New Jersey/76 (Hsw1N1).

Between December 2005 and February 2009 only 12 isolated cases of swine influenza transmitted to humans have been reported (CDC, Atlanta, Ga).


Although the diagnosis of Influenza A (H1N1) is hard due to the similarity of its symptoms with those of other respiratory infections, in particular with seasonal influenza; these are generally fever, cough, sore throat, nasal congestion or runny nose, body aches, headache, chills and fatigue, and a lower number of people may experiment diarrhea and vomiting.

There are certain signs of alarm that must orient the immediate search of medical attention, with or without a confirmed influenza diagnostic, among them: Confusion or sleepiness, coughing up phlegm with blood, difficulty breathing and chest pains. These occur more frequently in groups with a higher risk of catching Influenza A (H1N1) and developing complications similar to the ones caused by seasonal influenza. These high risk groups are constituted by:

  • People under 5 years and over 65 years of age
  • Pregnant women
  • People with medical concomitant conditions, for example: asthma, diabetes, heart and lung diseases, etc.
  • People with a deficient immune system (defenses), for example: AIDS, in chemotherapy for cancer and other diseases.
  • Elderly held in nursing homes and personnel that works in them.

Ideally, everyone with the symptoms mentioned previously, should be tested in a laboratory to confirm the diagnostic. For that, an evaluation by the family doctor is necessary, who if considers the possibility of influenza must take 2 samples of nasal swabbing, aspirated or washed, to perform 2 tests: The first one must be processed immediately (RT-PCR) and will serve to determine if the respiratory infection is or is not Influenza A or B and the second one should be put in a special tube (transportation) and be kept in the laboratory under special conditions so that, in case the first sample is positive for Influenza A, it is sent and processed by the Ministry of Health to determine if it is the subtype H1N1. In case both are positive we will be before a confirmed case.

TREATMENT: There are 4 antivirals approved for treatment and prevention of infections caused by the Influenza virus, 2 belong to those called M2 inhibitors (Amantadine and Rimantadine) and two to the inhibitors of Neuraminidase (Oseltamivir and Zanamivir). Laboratory tests done in the United States with the Influenza A (H1N1) virus have allowed to determine that this virus is only sensitive to Oseltamivir (Tamifluâ) and Zanamivir (Relenzaâ).

With the intention of obtaining the greatest effectiveness of these antivirals, they must be administered timely, that is, within the first 2-3 days since the disease has started. However, its use can also be considered even after 3 days, particularly in hospitalized patients and in people with a high risk of developing complications associated to influenza. Observing this recommendation, these antivirals can decrease the intensity of the symptoms, shorten the duration of the disease and reduce the frequency of complications. Unfortunately, world production of these antivirals, particularly Oseltamivir, would not be enough to cover the necessities of the world population in presence of a pandemic, so it will have to be reserved for the people with a confirmed diagnosis of Influenza A (H1N1), and very specially for those patients included in the high risk groups.

The use of antibiotics is not indicated during the acute stage of the disease, but it is in case bacterial complications appear. Other pharmaceuticals can be considered, especially those that provide symptom relief, such as antipyretics (acetaminophen, dexketoprofen or diclofenac), antitussives, hydration salts, etc.

PREVENTIVE MEASURES: In the approach of pandemics it is important to observe certain hygiene measures, which have as a main objective to limit the spread of germs. Among them, the most important ones are:

  • Frequently wash your hands and wrists with clean running water and soap, preferably liquid, especially if your hands are dirty, you have been in the bathroom or if you have had contact with respiratory secretions.
  • Rub your hands with 70% alcohol-based gel disinfectants. This measure, although more expensive, is effective when there are no clean bathrooms properly implemented.
  • When sneezing, blowing your nose, or coughing, cover your mouth with tissues, preferably disposable. In absence of disposable tissues, you can use cloth tissues or even the sleeve of your shirt. Later, dispose of the used tissues, depositing them in a trash can and do not throw them on the floor or on the street.
  • Avoid touching eyes, nose and mouth to reduce the risk of transmitting the virus.
  • If you have symptoms that suggest acute respiratory infection, stay at home, avoid close contact with healthy people and consult your doctor or the community health service to establish the origin of your illness. If the influenza diagnostic is confirmed, you must stay at home for at least 7 days and up to 24 hours after the symptoms have disappeared.
  • Keep an appropriate distance, around 2 to 2.5 meters or feet, from everyone who manifests symptoms of respiratory infection.
  • Avoid greeting with a kiss, handshake or hug.
  • Do not share food, cups or cutlery.
  • Ventilate and allow the sun to enter your house, office and every closed space.
  • Keep all everyday objects clean, for example: kitchen cutlery, bathroom utensils, door handles, handrails, telephones, toys, and other commonly used objects.
  • The cleaning staff of public institutions, under normal conditions should wear gloves (latex, polyurethane or polyethylene), to avoid infections.
  • Consider the use of masks: Generally, the first thing that comes to mind when there is a risk of acquiring an air-borne infection is the use of masks. Unfortunately, it is not judged that its effectiveness in preventing the transmission of the influenza virus is unknown. Its use, not completely justified, lies in that when used correctly, these can contribute to stop the dissemination of saliva drops when the people that wear them speak, cough, or sneeze, or to get a certain benefit when being exposed to sick people. The use of a mask must not deviate attention from the recommendations described before.

Below, some recommendations that can increase the effectiveness of masks:

  • First, avoid close contact, less than 2-2.5 meters or 6 ft., with a person with a probable or confirmed influenza diagnostic, be it seasonal or pandemic.
  • If the previous condition is inevitable, wear tightly adjusted masks, covering nose and mouth, not allowing empty spaces between these and the skin. Ideally, ask for advice from your doctor about its use.
  • Although surgical masks may be used, the ones that have proven to have a highest utility degree are the ones called N95.
  • Its use is particularly indicated in high risk groups (see diagnosis).
  • Remember masks are disposable and are not to be interchanged with other people, after being used must be disposed of in a trash can with a lid, ideally after being placed in a sealed bag.

VACCINATION: Regarding vaccination, this is one of the most highly effective practices to reduce the disease and death by influenza, and can bring protection to a greater number of people in the world. Unfortunately at this moment there is no vaccine commercially available against the new subtype H1N1, but it is already being worked on and it is been mentioned that it could be available in 4-6 months. While this moment comes, observation and application of preventive measures is vital.

About the vaccine against seasonal influenza, preliminary analysis done by the serum of vaccinated and immunized people, done by CDC (Centers for Disease Control and Prevention, Atlanta, GA), indicate that this does not protect against influenza A (H1N1) virus. Not because of this its administration should be abandoned, given its important role in the prevention of an infection that causes 3 to 5 million of sick people and from 250,000 to 500,000 deaths per year in the whole world, according to figures from the WHO.

Therefore, in the face of the growing number of cases in our country, it would be good to increase our attention to the early recognition of the disease, its immediate management, and most importantly yet, observe and carry out the preventive measures previously pointed out. For more information, you can visit the following sites on the internet:,