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From Medscape Infectious Diseases > Jarvis on Infectious Disease
Influenza Surveillance: Lessons Learned From Hong Kong
William R. Jarvis, MD
Posted: 11/17/2010
Hi, this is Dr. William Jarvis, Medscape Infectious Diseases expert advisor, and President of Jason and Jarvis Associates. As we're about to enter influenza season, I thought that it would be interesting to reduce some data from Hong Kong, where they have fantastic surveillance systems for influenza, in particular, for H1N1.
Until September 2009, virtually every patient who had influenza-like illness was tested for H1N1, and they compared their data on patients tested when everybody was tested vs after that, when they only tested for 6 different indications. The first period had almost 27,000 patients and the second period about 36,000 patients, and they found that patients who fell into the "seriously ill" category was 0.4% when everyone was tested and about twice that (0.7%) when only the top 6 indications were tested. The difference was not significant.
Of interest, intensive care unit admissions were the same during both of those time periods; about 69% and 70%. The case-fatality rate, which is a much better estimate than we have in the United States, for the initial period -- when everyone was tested for H1N1 -- was 0.1%. In the second period, when only the 6 indications were tested, it was higher (0.21%), which probably tells us that when you don't test everyone, you're missing patients who actually have influenza and who may have died of influenza. This compares with the 0.6% reported in the United States. I think it shows that when everyone is tested, the mortality rate associated with H1N1 (0.1%) is actually very low.
They also reported data on healthcare workers. During the initial period of the H1N1 pandemic, all clinical and nonclinical personnel were tested if they developed signs and symptoms of influenza. They had mandatory reporting of influenza. The clinical personnel attack rate was 0.62% and nonclinical was 0.63%, so after the first 2 months, when they found that there was really no significant difference between clinical and nonclinical personnel, they limited the mandatory reporting to only clinical personnel.
Clearly the data show that where they're only using masks (not respirators), there was no significant increased risk to healthcare personnel who were clinically active vs those who had no clinical responsibilities. Subsequently, they did serologic studies of the population and found that, in fact, the prevalence was higher (3.5%) in the general population than in clinical personnel (2.6%).
When they tested clinically active vs nonclinical personnel serologically, 12% of clinical personnel were positive, whereas nonclinical personnel were positive 14% of the time. What they've shown is that there were no clinical activities that increased the risk for influenza when appropriate protection, including a surgical mask, was used. In contrast, if there was unprotected contact (eg, no mask used during clinical care), that was when healthcare workers were most at risk of acquiring influenza.
I think going into this influenza season we know several things. First, we should do our best to immunize our healthcare workers against influenza, and second, if you're clinically taking care of patients, then you should be wearing at least a surgical mask to protect yourself from H1N1.
Until next time, this is Dr. William Jarvis, President of Jason and Jarvis Associates. Thank you very much.
Web Resource
Hong Kong Centre for Health Protection. Available at: http://www.chp.gov.hk/en/index.html Accessed November 9, 2010.
http://www.medscape.com/viewarticle/732629
Influenza Surveillance: Lessons Learned From Hong Kong
William R. Jarvis, MD
Posted: 11/17/2010
Hi, this is Dr. William Jarvis, Medscape Infectious Diseases expert advisor, and President of Jason and Jarvis Associates. As we're about to enter influenza season, I thought that it would be interesting to reduce some data from Hong Kong, where they have fantastic surveillance systems for influenza, in particular, for H1N1.
Until September 2009, virtually every patient who had influenza-like illness was tested for H1N1, and they compared their data on patients tested when everybody was tested vs after that, when they only tested for 6 different indications. The first period had almost 27,000 patients and the second period about 36,000 patients, and they found that patients who fell into the "seriously ill" category was 0.4% when everyone was tested and about twice that (0.7%) when only the top 6 indications were tested. The difference was not significant.
Of interest, intensive care unit admissions were the same during both of those time periods; about 69% and 70%. The case-fatality rate, which is a much better estimate than we have in the United States, for the initial period -- when everyone was tested for H1N1 -- was 0.1%. In the second period, when only the 6 indications were tested, it was higher (0.21%), which probably tells us that when you don't test everyone, you're missing patients who actually have influenza and who may have died of influenza. This compares with the 0.6% reported in the United States. I think it shows that when everyone is tested, the mortality rate associated with H1N1 (0.1%) is actually very low.
They also reported data on healthcare workers. During the initial period of the H1N1 pandemic, all clinical and nonclinical personnel were tested if they developed signs and symptoms of influenza. They had mandatory reporting of influenza. The clinical personnel attack rate was 0.62% and nonclinical was 0.63%, so after the first 2 months, when they found that there was really no significant difference between clinical and nonclinical personnel, they limited the mandatory reporting to only clinical personnel.
Clearly the data show that where they're only using masks (not respirators), there was no significant increased risk to healthcare personnel who were clinically active vs those who had no clinical responsibilities. Subsequently, they did serologic studies of the population and found that, in fact, the prevalence was higher (3.5%) in the general population than in clinical personnel (2.6%).
When they tested clinically active vs nonclinical personnel serologically, 12% of clinical personnel were positive, whereas nonclinical personnel were positive 14% of the time. What they've shown is that there were no clinical activities that increased the risk for influenza when appropriate protection, including a surgical mask, was used. In contrast, if there was unprotected contact (eg, no mask used during clinical care), that was when healthcare workers were most at risk of acquiring influenza.
I think going into this influenza season we know several things. First, we should do our best to immunize our healthcare workers against influenza, and second, if you're clinically taking care of patients, then you should be wearing at least a surgical mask to protect yourself from H1N1.
Until next time, this is Dr. William Jarvis, President of Jason and Jarvis Associates. Thank you very much.
Web Resource
Hong Kong Centre for Health Protection. Available at: http://www.chp.gov.hk/en/index.html Accessed November 9, 2010.
http://www.medscape.com/viewarticle/732629