H1N1: Insights From ATS 2009
H1N1: Insights From ATS 2009
Hello. My name is Dr. Christopher Lettieri and today I'm going to have a brief discussion on human influenza virus A (H1N1), or swine flu. In mid-March of this year, sporadic cases of H1N1 were reported in Mexico. By mid-April, the number of cases had dramatically increased and involved patients in several different countries. As of today, there have been just under 10,000 confirmed cases in 41 countries, resulting in 76 deaths worldwide. In the United States, there have been nearly 5500 cases and 6 deaths. H1N1 is a novel strain of human influenza virus which has achieved the characteristics to be labeled a pandemic. The term "pandemic" is often used inappropriately; it is important for the medical community to use this terminology correctly so that we can ensure proper communication.
Pandemic
Outbreaks of infectious diseases can either be endemic or pandemic. "Endemic" refers to those diseases that are constantly present in a specific community, like our common influenza virus. Pandemics, on the other hand, are infectious diseases that impact extensive geographic regions, affecting a large population of patients. For purposes of pandemic flu planning, this is defined as 2 or more countries. For a pandemic to occur, the infectious agent must evolve and develop the ability to cause disease in humans, result in serious infection, and lead to sustained human-to-human transmission. H1N1 has achieved all 3 of these characteristics.
We should be reminded that there have been 3 prior influenza pandemics in the past century. The Spanish flu of 1918 resulted in 20-40 million deaths worldwide and the Asian flu of 1957 and the Hong Kong flu of 1968 each resulted in 2-5 million deaths. While H1N1 has not yet led to a significant number of deaths, any novel strain of influenza has the potential to lead to a global impact. Human influenza represents an annually occurring endemic infection with worldwide threat. In the United States, influenza leads to 100,000 hospitalizations and 65,000 deaths annually, making it the seventh leading cause of death among Americans. However, the majority of deaths are confined to persons over the age of 55 and occur after primary or secondary pneumonias.
H1N1 Influenza Characteristics
On a molecular level, H1N1 does not possess the qualities common to highly virulent strains, and hospitalization and mortality rates seen so far are similar to those for commonly occurring influenza. As such, it does not appear to be a highly virulent pathogen. However, as I stated, any novel strain still has the potential to have a global impact. While death rates do not appear to be significant yet, H1N1 has some characteristics that are concerning. The first is that the disease is occurring in those who have been previously immunized. Obviously, this means that the immunizations that have already been received are either ineffective or partially ineffective. However, there's concern that it increases susceptibility. In healthcare workers, who are almost universally immunized, we see an increased prevalence of disease occurring, thereby suggesting that prior immunizations may increase susceptibility to H1N1. However, this has not yet been substantiated.
Another concern and characteristic of H1N1 is that significant disease is not limited to the extremes of age. In Mexico, the mean age of those with confirmed cases was 35 years, with 75% of cases occurring in those between 20 and 55 years of age. In the United States, 80% of cases have been in patients 5-40 years old.
Diagnosis
H1N1 is diagnosed the same way as any other strain of influenza and often has similar symptoms. However, in both Mexico and the United States, more gastrointestinal symptoms have been reported, which may decrease clinicians' suspicions that this is actually influenza. Like any other strain of influenza, H1N1 has a 1- to 4-day latency after infection, followed by 5-7 days of symptoms. It should be noted that, as with other causes of influenza, H1N1 is infectious for not only the 1- to 4-day latent period but also for several days after the onset of symptoms, and it may continue to have viral shedding after the defervescence of fever.
Rapid testing should be widely used in patients presenting with influenza-like illnesses. Commercially available tests have a sensitivity of 70% and specificity of over 90%. While this is good, it still represents a high false-negative rate. To aid in the confirmation of cases, the CDC has made real-time polymerase chain reaction (PCR) tests available to all public health laboratories using their emergency response authority.
Treatment
When confirmed or highly suspected, directed therapy should be considered. Treatment of influenza will reduce the duration of symptoms, decrease the risk for complications, and reduce viral shedding, and, therefore, infectivity. However, most cases are self-limited, and there must be a balance between the benefits of treatment and the expense and potential toxicity of medications. As such, the CDC currently recommends that treatment be confined to high-risk patients, those at extremes of age, or with significant underlying comorbid conditions, particularly chronic lung diseases.
Two medications are currently recommended in the treatment of influenza: oseltamivir and zanamivir. Oseltamivir (Tamiflu®) is given as an oral formation, 75 mg by mouth twice daily for 5 days. Zanamivir (Relenza®) is available as a dry inhalational powder and is given as two 5-mg doses (2 oral inhalations) twice daily for 5 days. To be effective, treatment should begin as soon as possible, and definitely within the first 48 hours of onset of symptoms.
Impact on Healthcare Workers
As with other emerging diseases, the impact on healthcare workers is concerning. Healthcare workers can become infected themselves, may have to stay home to care for infected family members, or may be fearful of contracting the infection themselves. There is concern with any emerging infectious disease that we will have limited healthcare workers available to care for patients who become infected. In Mexico, 41 healthcare workers have had confirmed cases of H1N1. In the United States, 82 healthcare workers have also been confirmed to have H1N1, the majority of which have received prior immunizations. In the United States, all 82 cases are thought to have contracted the infection in the community and not as a direct result of patient care. In Mexico, numerous healthcare workers, particularly nurses, refused to come to work or refused to care for particular patients. We have not yet encountered this in the United States, but this is a concern -- not only of H1N1, but of any emerging infectious disease.
Conclusion
H1N1 represents a novel strain of influenza virus that does not appear to be more virulent than commonly circulating strains of influenza. However, as stated, there are some characteristics that are concerning, and the impact of this virus will be better understood as the southern hemisphere enters into its flu season. For now, the CDC recommends separation of patients with influenza-like illness from the general population and the proper use of droplet precautions. The liberal use of testing of any patient presenting with influenza-like illness should be done, and directed therapy, especially for high-risk patients, should be considered.
This is Christopher Lettieri for Medscape. Thank you very much for watching.
Hello. My name is Dr. Christopher Lettieri and today I'm going to have a brief discussion on human influenza virus A (H1N1), or swine flu. In mid-March of this year, sporadic cases of H1N1 were reported in Mexico. By mid-April, the number of cases had dramatically increased and involved patients in several different countries. As of today, there have been just under 10,000 confirmed cases in 41 countries, resulting in 76 deaths worldwide. In the United States, there have been nearly 5500 cases and 6 deaths. H1N1 is a novel strain of human influenza virus which has achieved the characteristics to be labeled a pandemic. The term "pandemic" is often used inappropriately; it is important for the medical community to use this terminology correctly so that we can ensure proper communication.
Pandemic
Outbreaks of infectious diseases can either be endemic or pandemic. "Endemic" refers to those diseases that are constantly present in a specific community, like our common influenza virus. Pandemics, on the other hand, are infectious diseases that impact extensive geographic regions, affecting a large population of patients. For purposes of pandemic flu planning, this is defined as 2 or more countries. For a pandemic to occur, the infectious agent must evolve and develop the ability to cause disease in humans, result in serious infection, and lead to sustained human-to-human transmission. H1N1 has achieved all 3 of these characteristics.
We should be reminded that there have been 3 prior influenza pandemics in the past century. The Spanish flu of 1918 resulted in 20-40 million deaths worldwide and the Asian flu of 1957 and the Hong Kong flu of 1968 each resulted in 2-5 million deaths. While H1N1 has not yet led to a significant number of deaths, any novel strain of influenza has the potential to lead to a global impact. Human influenza represents an annually occurring endemic infection with worldwide threat. In the United States, influenza leads to 100,000 hospitalizations and 65,000 deaths annually, making it the seventh leading cause of death among Americans. However, the majority of deaths are confined to persons over the age of 55 and occur after primary or secondary pneumonias.
H1N1 Influenza Characteristics
On a molecular level, H1N1 does not possess the qualities common to highly virulent strains, and hospitalization and mortality rates seen so far are similar to those for commonly occurring influenza. As such, it does not appear to be a highly virulent pathogen. However, as I stated, any novel strain still has the potential to have a global impact. While death rates do not appear to be significant yet, H1N1 has some characteristics that are concerning. The first is that the disease is occurring in those who have been previously immunized. Obviously, this means that the immunizations that have already been received are either ineffective or partially ineffective. However, there's concern that it increases susceptibility. In healthcare workers, who are almost universally immunized, we see an increased prevalence of disease occurring, thereby suggesting that prior immunizations may increase susceptibility to H1N1. However, this has not yet been substantiated.
Another concern and characteristic of H1N1 is that significant disease is not limited to the extremes of age. In Mexico, the mean age of those with confirmed cases was 35 years, with 75% of cases occurring in those between 20 and 55 years of age. In the United States, 80% of cases have been in patients 5-40 years old.
Diagnosis
H1N1 is diagnosed the same way as any other strain of influenza and often has similar symptoms. However, in both Mexico and the United States, more gastrointestinal symptoms have been reported, which may decrease clinicians' suspicions that this is actually influenza. Like any other strain of influenza, H1N1 has a 1- to 4-day latency after infection, followed by 5-7 days of symptoms. It should be noted that, as with other causes of influenza, H1N1 is infectious for not only the 1- to 4-day latent period but also for several days after the onset of symptoms, and it may continue to have viral shedding after the defervescence of fever.
Rapid testing should be widely used in patients presenting with influenza-like illnesses. Commercially available tests have a sensitivity of 70% and specificity of over 90%. While this is good, it still represents a high false-negative rate. To aid in the confirmation of cases, the CDC has made real-time polymerase chain reaction (PCR) tests available to all public health laboratories using their emergency response authority.
Treatment
When confirmed or highly suspected, directed therapy should be considered. Treatment of influenza will reduce the duration of symptoms, decrease the risk for complications, and reduce viral shedding, and, therefore, infectivity. However, most cases are self-limited, and there must be a balance between the benefits of treatment and the expense and potential toxicity of medications. As such, the CDC currently recommends that treatment be confined to high-risk patients, those at extremes of age, or with significant underlying comorbid conditions, particularly chronic lung diseases.
Two medications are currently recommended in the treatment of influenza: oseltamivir and zanamivir. Oseltamivir (Tamiflu®) is given as an oral formation, 75 mg by mouth twice daily for 5 days. Zanamivir (Relenza®) is available as a dry inhalational powder and is given as two 5-mg doses (2 oral inhalations) twice daily for 5 days. To be effective, treatment should begin as soon as possible, and definitely within the first 48 hours of onset of symptoms.
Impact on Healthcare Workers
As with other emerging diseases, the impact on healthcare workers is concerning. Healthcare workers can become infected themselves, may have to stay home to care for infected family members, or may be fearful of contracting the infection themselves. There is concern with any emerging infectious disease that we will have limited healthcare workers available to care for patients who become infected. In Mexico, 41 healthcare workers have had confirmed cases of H1N1. In the United States, 82 healthcare workers have also been confirmed to have H1N1, the majority of which have received prior immunizations. In the United States, all 82 cases are thought to have contracted the infection in the community and not as a direct result of patient care. In Mexico, numerous healthcare workers, particularly nurses, refused to come to work or refused to care for particular patients. We have not yet encountered this in the United States, but this is a concern -- not only of H1N1, but of any emerging infectious disease.
Conclusion
H1N1 represents a novel strain of influenza virus that does not appear to be more virulent than commonly circulating strains of influenza. However, as stated, there are some characteristics that are concerning, and the impact of this virus will be better understood as the southern hemisphere enters into its flu season. For now, the CDC recommends separation of patients with influenza-like illness from the general population and the proper use of droplet precautions. The liberal use of testing of any patient presenting with influenza-like illness should be done, and directed therapy, especially for high-risk patients, should be considered.
This is Christopher Lettieri for Medscape. Thank you very much for watching.
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