AN UNEXPECTED EPIDEMIC?THE H1N1 EXPERIENCE

IN MEXICO

Dr. Marlene Llópiz AvilésAustin College

Sherman, TexasNovember 2009

Definitions

Individuals who are infected and show either no or only mild symptoms are said to have a subclinical infection.

Subclinically infected individuals with no symptoms are identified as well-carriers of the disease because they are carrying and frequently shedding the disease agent.

The incubation period (time between exposure and the first detectable symptom), latency period (time when the disease is concealed, hidden, or inactive), and infectious period (time during which the disease can be transmitted with or without contact) for several common diseases.

Definitions The prevalence of a disease is the number of diseased individuals at any one

time (point prevalence) or over a given period (period prevalence).

The incidence is the number of new cases of a disease that occur within a defined population over an established period of time. Frequently either prevalence or incidence, or both, are given as a rate, meaning the number of cases in a fixed number of people, e.g., cases per 100,000.

Individual cases of disease in widely separated geographic areas or otherwise independent cases are said to be sporadic.

Any excessive and related incidence of a particular disease above what is normally expected in a population is defined to be an epidemic. When an epidemic extends beyond the confines of a wide area, typically a continent, and becomes a more widespread problem, it is a pandemic.

History of Influenza Epidemics

Hippocrates seems to have been the first observer to record an influenza pandemic in the year 412 B.C.

Since 1580, there have been thirty-one additional flu pandemics recorded.

History of Influenza Epidemics

At Camp Funston (now Fort Riley) in Kansas on the morning of March 11, 1918, Albert Mitchell, a company cook, reported to the infirmary complaining of a low-grade fever, sore throat, headache, and muscle aches—typical flu symptoms. He was sent to bed.

By noon of that day, 107 soldiers exhibited similar symptoms and within two days, a total of 522 people were sick. Some were close to death with severe pneumonia. (Remember, there were no antibiotics in general use until the 1950s.)

Camp Funston was the tip of the iceberg as other military bases reported similar figures almost immediately. Even shipboard sailors docked off the East Coast were affected.

Within a week even isolated locales were hit; the island of Alcatraz reported cases. No state escaped infection. Neither was the disease held in check by the vast expanse of ocean; by April, French soldiers and civilians were infected.

Within two weeks, it had spread to China and Japan. During May it was found in Africa and South America. By this time, it had eased its burden of illness and death on the Americas, but continued its onslaught elsewhere. This first wave, somewhat more than a minor annoyance, was more deadly than the typical flu, but far from what was to be seen.

History of Influenza Epidemics During the autumn of 1918, likely after experiencing antigenic shift, the flu

reappeared in the Americas. This time it seemed more virulent and continued to attack people in the 19-34 age group along with the usual population segments of children and the elderly. Fully 20% of the population was affected.

Deaths from pneumonia were unusually high. At military camps bodies could not be autopsied fast enough that the dead were piled like so much cordwood in storerooms.

The civilian population was also decimated. Medical personnel were unable to offer more than palliative care. Some medical authorities claimed the cause was "Pfeiffer's bacillus" and recommended wearing gauze masks to prevent its spread. Schools and public places were closed. Many cities mandated the wearing of masks and levied fines of $5 on those who failed to comply.

History of Influenza Epidemics The disease's effect on military age men was so great that the American draft was

suspended in October of 1918 due to the epidemic.

As the Allies engaged Germany in a series of "final" offensives, the flu was a major player in the overall mortality rate and swung the outcome of some battles. Even General Pershing, the commander of the American Expeditionary Force (AEF, impolitely referred to as ass-end-first by the common foot soldier) was affected. So many soldiers died of it, that the flu had a significant influence on the cessation of hostilities.

The AEF suffered 35,000 battle-related casualties and 9,000 deaths from flu. Of course, this means that many, many more soldiers had been unable to fight because of the disabling disease.

Even the peace conference at Versailles was affected as all three major participants, President Woodrow Wilson of the United States, Prime Minister David Lloyd George of Great Britain, and Premier Georges Clemenceau of France, contracted the disease and this likely changed the outcome of the negotiations.

History of Influenza Epidemics About eighteen months after its first appearance, the disease disappeared.

At its height, mortality rates were 15.8% in Philadelphia, 14.8% in Baltimore, and 10.9% in Washington D.C. Sixty percent of the Inuit population in Nome, Alaska fell victim to the flu.

Although overall death rates were relatively low, the incidence rate was abnormally high at around 20% of the population. Almost everyone in this country knew of someone who had succumbed to the flu.

Between 80% and 90% of the Western Samoan population (under the governance of New Zealand) was infected.

The U.S. death toll was 650,000—low by worldwide standards; Russia lost 450,000; Italy 375,000; Britain 228,000; 500,000 in Mexico; 44,000 in Canada; unnumbered millions died in the Asian subcontinent. Estimates of the worldwide mortality for this epidemic range from 25 million to 50 million.

The unusual feature of this epidemic was the age-mortality curve: flu usually kills young children and the elderly, but this version also took a large proportion of males between 19 and 34. Compared to the Plague of the Middle Ages with its eight to thirteen million dead globally per year, this may have been the most lethal recorded epidemic in human history.

History of Influenza Epidemics

December of 1997 saw a minor eruption of an avian flu in Hong Kong. In the manner of Falstaff's suggestion for curing the ills of society, they began by killing all the chickens.

As of January 1, 2001, it has not been incontrovertibly established that that variant of the disease can be spread from human-to-human, although there may have been one or two such cases.

During September of 2001 it was announced that the full genome of the 1918 flu had been decoded and the protein that caused its virulence had been discovered.

It was an H1N1 flu.

The H1N1 Virus

Influenza is caused by a virus that is readily spread by aerosol droplets.

The Virus

The outside of the virion is covered with two kinds of spikes: about 500 H spikes (hemaggluttin), which work to initiate infection, and about 100 N spikes (neuraminidase), which release the virus from the cell surface and allow it to infect other cells.

The Virus Reassortment, or Viral Subunit

Reassortment, is the exchange of DNA between viruses inside a host cell. Two or more viruses of different strains (but usually the same species) infect a single cell and pool their genetic material creating numerous genetically diverse progeny viruses.

It is a type of genetic recombination.

Reassortment can lead to a viral shifts under some conditions.

How the Virus Works

What happened in Mexico? March 18

Cases of influenza-like illness begin to be noted by health authorities in Mexico. Thought to be an extension of the seasonal influenza period.

April 9Close friend calls and reports a number of cases of influenza like non-typical cases in San Luis Potosí.

April 12An outbreak of influenza-like illness is reported in the state of Veracruz, Mexico, east of Mexico City. Similar cases in California

April 17A case of atypical pneumonia in the state of Oaxaca, Mexico, in the south of the country, is reported. Mexican health authorities ask hospitals to report all cases of severe respiratory illness and collect laboratory specimens from them.

What happened in Mexico? April 23

Following a steady rise, a total of 854 cases of pneumonia, presumably resulting from influenza-like illness, have been reported in Mexico City with 59 deaths.

Meanwhile, in San Luis Potosí, Mexico, north of Mexico City, 24 cases of influenza-like illness with 3 deaths have be reported, and in Mexicali, just south of California, four cases of influenza-like illness with no deaths have been reported.

These flu-like illnesses affected more healthy young adults and fewer of the very young and elderly than typical flu does. Several of them are laboratory confirmed as swine-origin influenza A (H1N1) virus of the same genetic strain as that detected in two children in California.

What happened in Mexico?

April 23

The morning of April 23rd, the Minister of Health of Mexico was interviewed on the radio and he said everything was under control and things were fine.

The evening (11 p.m.) of April 23rd the same Minister of Health declared schools in Mexico City to be closed until further notice, to avoid crowded places, to use surgical masks, and to practice intense hand-washing.

What happened in Mexico?

April 25By this day, there are 1004 cases and 68 deaths in Mexico.

April 26CDC reports 20 laboratory confirmed human cases of swine influenza A/H1N1 from across the entire continental United States. All are classified as mild influenza like illness with no deaths reported. Preliminary testing shows all have the same genetic makeup, and the virus is described as a new subtype of influenza A H1N1.

Mexican government reports 18 laboratory confirmed cases of swine influenza A/H1N1, with possible cases reported in 19 of the country's 32 states.

What happened in Mexico?

April 27There are 1384 cases and 81 deaths reported in Mexico. Phase 4 is declared.

Schools are closed in the entire country, restaurants, movie theaters, churches, stadiums, etc. are closed until further notice.

CDC lab confirmed human cases total 40 (0 deaths). Canada reports 6 cases (0 deaths). Spain reports 1 case (0 deaths).

What happened in Mexico? April 29

A total 148 laboratory-confirmed cases are reported in 9 countries; most of these are in the U.S. (91) and Mexico (26). There is only one new death, in the United States. New countries reporting infections are Austria and Germany.

1,890 cases are reported in Mexico with 145 deaths.Dr. Margaret Chan raises the level from phase 4 to 5.

Presidential announcement requests everyone stay home.

Body temperature detectors are installed at the airport.Mexicans are quarantined in China.

What happened in Mexico? April 30

A total of 11 countries now report lab-confirmed cases. The total for the United States is 109. New countries reporting infections are the Netherlands and Switzerland.

Total H1N1 cases in Mexico: 1,918 suspected (i.e. patients with flu-like illness), 286 of which are probable (i.e. test positive for influenza A) and 97 of which are confirmed (i.e. laboratory genetic testing confirms swine influenza A/H1N1).

Mexico's Health Secretary José Angel Córdova expresses "optimism" based on the stabilization of the number of new confirmed cases in Mexico, noting that the data from the next few days will be "critical."

What happened in Mexico? May 1

A total of 13 countries now report lab-confirmed cases totaling 365. Most of these are in Mexico (156), the United States (141), and Canada (34). New countries reporting infections are China (Hong Kong) and Denmark.

Two more lab-confirmed deaths are reported in Mexico for a total of nine.

May 2A total of 16 countries now report a total of 658 lab-confirmed cases. The total in Mexico is 397, with health officials there noting that the apparent sudden increase from the previous day is indicative of test results coming back, not of a sudden jump in the number of illnesses. Mexico now reports 16 lab-confirmed H1N1 swine flu deaths.

The United States total is now 160 cases and the Canada total is 51 cases. All other countries report 15 or fewer cases each. New countries reporting lab-confirmed cases are Costa Rica, France, and South Korea.

What happened in Mexico? June 11

Influenza goes from phase 5 to 6

June 29Argentina reports its first cases.Schools and restaurants are closed.

July-AugustFirst pilot lots of a vaccine may become available for testing.

November-January 2010As ordered by health officials, enough vaccine may be produced for large-scale vaccination in the U.S. , not so for Mexico.

Only 30% of the total number of expected vaccines are to be delivered to Mexico by the end of November – beginning of December.

Symptoms

The disease is characterized by a sudden onset:

Fever Chills Headache Muscle aches in the neck and back Prostration Cough and sore throat are also common.

Characteristics of the Disease Convalescence is slow and marked by fatigue and weakness. It is spread by

discharges from the mouth and noses of infected persons.

Young healthy adults appear to be particularly susceptible. There are usually more well-carriers than infected persons.

The mortality rate is usually only as high as 0.1%, but because the number

infected is so high, there is a significant excess mortality, usually due to pneumonia or other pulmonary complications.

In a typical year in the U.S. 20,000 people die of flu, more specifically bacterial pneumonia secondary to flu.

During heavy epidemic years the mortality figures can double. In the U.S., and

most temperate climates in the northern hemisphere, the disease usually peaks from December to March.

Treatment

Prevention

Hemispheric Impact

Should we worry?

Should we worry?

Should we worry?