General Pandemic/Avian FAQ
Answers to questions posed at the May, 2006 pandemic plan preview meetings.
Can you tell me more about the human-to-human transmission of H5NI? Regarding the 11- year old girl who died and her 26 year old unexposed mother who also died, were the mother and daughter exposed from the same original source (re infected bird feces, or was the mother infected by the daughter?
As of July 1, 2006, there have been two well documented instances of probable person-to-person transmission of avian influenza A H5N1. Other instances of possible transmission have also occurred. The first instance is described in detail in the January 27, 2005 issue of the New England Journal of Medicine (Ungchusak et. al.; 352:333-340).
An 11-year old girl in Thailand who lived with her aunt presented to a clinic with fever, cough, and a sore throat on September 2, 2004. She was admitted to a hospital on September 7 with a fever and moderate dyspnea. Because of progressive respiratory distress, hypoxemia, and shock, she was transferred to a provincial hospital the next day. Despite mechanical ventilation, administration of broad-spectrum antibiotics, and fluid resuscitation, the patient died 3 hours after admission to the provincial hospital. She is likely to have had H5N1 influenza. She was not known to have had direct contact with her family’s sick or dying chickens, but she played and slept in an area where the chickens were also often present. Her mother lived and worked in a province 4 hours' drive from her daughter's village.
The mother provided bedside care for her daughter in the hospital for 16 to 18 hours on September 7 and 8. She began to have fever and headache 3 days later and spent a night in her daughter's village before returning to her home. On September 17, she was admitted to a hospital in her own province with fever and severe dyspnea. Pneumonia and progressive respiratory failure were diagnosed, and she died on September 20. Post-mortem specimens tested positive for H5N1.
The child's aunt provided bedside care for her niece for 12 or 13 hours on September 7 and noted the onset of fever, myalgia, and chills on September 16. An upper respiratory infection was diagnosed at a clinic on September 19, but she had progressive difficulty breathing and was admitted to the district hospital on September 23 with a high fever, lymphopenia, and left-lower-lobe consolidation. On the day of admission, an investigating team suspected avian influenza, obtained respiratory specimens for testing, initiated treatment with oseltamivir, and instituted full isolation precautions. Despite moderate dyspnea and hypoxemia, her condition gradually improved, and she was discharged on October 7. Specimens from her later tested positive for H5N1.
From the time the girl became ill until the arrival of her mother at the hospital, the aunt provided much of her care, including bedside care on September 7. The girl's mother lived in a Bangkok suburb with her husband, but they drove to the province on learning of her daughter's hospitalization. They stopped at the household for less than 10 minutes to pick up a document and arrived at the hospital at about midnight. The mother then provided bedside care for the next 16 to 18 hours, and nurses later reported that she sat on the bed, hugged and kissed her daughter, and wiped secretions from her mouth.
A second instance of probable person-to-person transmission was recently documented near Sumatra, Indonesia. A woman contracted influenza and died through exposure to infected poultry. Seven other family members became ill and six died. All had close exposure to the woman and all were shown to have the same genetically related virus. The virus had mutated slightly in a 10-year old boy, who died, and he passed it on to his father who also died. More information can be found on the World Health Organization website (http://www.who.int)
Why is the flu most of the time fatal to 20-40 year old health adults? Is there any better explanation why the highest mortality rate was in the people ages 20-40? Is this the typical trend with a pandemic?
These questions are undoubtedly referring to the 1918 influenza pandemic when more than half the deaths occurred among largely healthy people between 18 and 40 years of age. It is thought that the extreme morbidity and mortality were caused by a virus-induced cytokine storm that led to the acute respiratory distress syndrome (ARDS). This age group has a stronger immune system that may have contributed to the cytokine storm. The ARDS-related morbidity and mortality in the pandemic of 1918 was on a different scale from those of influenza pandemics of 1957 and 1968, a fact that highlights the importance of the virulence of the virus subtype or genotype.
Are there any human populations who are at greater risk?
Presuming this question is asking about a future influenza pandemic, the answer will depend on many variables including the virus subtype, previous exposure (and therefore, immunity) to the virus subtype, cross-reacting immunity, virulence of the virus, and transmissibility.
To what extend do you think that level of medical care available to persons thus far affected by avian influenza has contributed to the high mortality rate?
In the current situation, most H5N1 patients who have died had been hospitalized in good medical facilities, and many had been treated with antivirals.
When a population experiences a shifted virus (pandemic situation) how long does it take to develop herd immunity?
There are too many unknown variables and complexities to answer this question.
How long does it take to progress through the six phases an influenza pandemic?
There are too many unknown variables to give a single answer to this question that would cover all situations.