2009 Pandemic H1N1 Influenza Epidemiology 
April 2009 – January 2010
Preliminary

Massachusetts has experienced two waves of H1N1 influenza.
Our surveillance data on influenza-like illness (ILI) through January 8, 2010 demonstrate a substantial peak in reports of illness in the late fall that exceed both the peak of H1N1 illness during the spring outbreak and the peak of the seasonal flu in the winter months during the past two flu seasons.  Slides 2 through 5 explain this surveillance data in detail.

Slide 2 Laboratory-confirmed (Culture & Rapid Tests) Influenza Cases & Influenza-Like Illness, Massachusetts 2008-2009
This slide shows the cycle of influenza last year, when the seasonal flu was the dominant strain.  As in most seasonal flu cycles, there were very few laboratory-confirmed cases of influenza during the summer and fall months, with the incidence of both laboratory-confirmed influenza cases and influenza-like illness (ILI) begin an upward slope in January and peaking first at the seventh week of the year (mid- to late-February) with around 2500 laboratory-confirmed cases in Massachusetts, and again around the twenty-second week of the year (mid-June), with about 2100 laboratory-confirmed cases in the state.  At the February peak, ILI comprised less than 4.5% of visits to doctors, and ILI made up less than 3% of doctor visits in the June peak.  Note that laboratory-confirmed cases of influenza are thought to be an underestimation of the true number of cases because most people will not be tested for influenza, especially around peaks, at which point physicians may assume ILI is influenza without additional testing.

Slide 3 Laboratory-Confirmed Influenza Cases and Influenza-Like Illness 
Massachusetts, October 4, 2009 – January 21, 2010 
Compare the previous slide to this one, showing laboratory-confirmed influenza cases between October 2009 and January 2010.  This period saw a peak in laboratory-confirmed influenza cases at the forty-fifth week of the year (mid-November), at 3600 cases.  At this peak, influenza-like illness (ILI) comprised about 10% of all doctors visits, over twice the rate of ILI-caused doctor visits in the highest 2008-2009 seasonal flu cycle.

Slide 4 Percentage of Influenza-Like Illness Visits Reported by Sentinel Provider Sites – Massachusetts
This slide compares the percentage of ILI-related doctor visits in Massachusetts during the current 2009-2010 cycle to the 2008-2009 and 2007-2008 cycles.  As noted in previous slides, ILI accounted for almost 10% of doctor visits in mid-November 2009; during the same time in 2008 and 2007, ILI accounted for around 1% of visits.  Also compare this peak to the mid-to-late-February peak in both 2009 and 2008, which reached only around 4.5%.  The 2007-2008 cycle also did not feature a mid-June second peak as the 2008-2009 cycle did.  This may suggest that the mid-June 2009 peak is not related to the seasonal flu cycle, and may have been part of the current H1N1 cycle.

Slide 5 Epidemiology/Surveillance
ILINet Cumulative Number of Standard Deviations Above Non Influenza Season Mean – H1N1Both Waves
April 26 – December 13, 2009
This slide compares the cumulative number of standard deviations for ILI above the baseline of non influenza season ILI doctor visits, across all 50 U.S. states, the District of Columbia, and Puerto Rico.  Massachusetts ranks the 21st lowest among this group in terms of ILI cases above the baseline for the period between April and December of each year, with a net number of standard deviation over baseline of 100.  Louisiana had the highest number of standard deviation over baseline, over 300, and Puerto Rico had the lowest, with zero change from the baseline. 

Slides 6 through 9 describe how H1N1 has affected different age groups in Massachusetts.

Slide 6 Age Distribution of Individuals Hospitalized with 2009 Pandemic H1N1 Influenza
in Years. Massachusetts, April 1, 2009 – January 5, 2010
Of 389 individuals hospitalized in Massachusetts with H1N1 between April 2009 and January 2010, 40% were between 5 and 24 years old, 23% were between 0 and 4 years, 19% were between 25 and 49, 12% between 50 and 64, and 6% were 65 years or older.

Slide 7 Age Distribution of Reported Influenza Cases in Massachusetts in the Spring and Fall of 2009
This graph compares the distribution of influenza cases by age in the Spring and Fall of 2009.  During the Spring, the plurality of cases (30%) impacted those between 5 and 12 years of age, but in the fall, the proportion of cases affecting that group dropped to 18%.  In the Fall, the plurality of cases (20%) affected those between 26 and 44.  The proportion was lowest in both Spring and Fall among those 65 and older, under 5% in both seasons.  It was almost the same (13%) for those between 0 and 4 in both seasons.  Among those between 13 and 18, it was higher in the Spring (18%) than the Fall (14%).  Among those between 19 and 25, it was higher in the Fall (13%) than the Spring (9%).  Among those between 45 and 64, it was higher in the Fall (17%) than the Spring (10%).

Slide 8 Age Distribution of Reported Influenza Cases in Massachusetts in the Spring and Fall of 2009
This graph displays the same information as the previous slide in a different way.

Slide 9 Rate of Hospitalization with Pandemic H1N1 Influenza by Age Group, per 100,000 Population
Massachusetts, April 1, 2009 to January 5, 2010
This slide shows H1N1 influenza hospitalization rate per 100,000 by age group, given the 389 people hospitalized between April 2009 and January 2010.  The rate for all ages was about 6 per 100,000.  Between 0 and 4 years of age, the rate was about 22.  Between 5 and 24 years of age, the rate was about 9. Between 25 and 49 years of age, the rate was about 3. Between 50 and 64 years of age, the rate was about 4. For those 65 and older, the rate was about 2.5.

Slides 10 through 18 show that members of racial and ethnic minorities bore a disproportionate burden of H1N1 disease and complications.

Slide 10 Distribution of Race/Ethnicity Categories Reported for Individuals Hospitalized with 2009 Pandemic H1N1 Influenza
Massachusetts, April 1, 2009 – January 5, 2010.
Among the 389 persons hospitalized for H1N1 influenza between April 2009 and January 2010, 41% were White, non-Hispanic, 14% were Black, non-Hispanic, 14% were Hispanic, 4% were Asian, 6% were Other, and 21% were Unknown.

Slide 11 Race/Ethnicity Among Individuals with Laboratory-Confirmed 2009 Pandemic H1N1 Influenza Compared to the Massachusetts Population
April 1, 2009 to January 5, 2010
Black, Hispanic and Asian residents were over-represented among confirmed cases compared to their percentages in the overall population.  This slide compares the percentage of the 1,959 laboratory-confirmed H1N1 influenza cases by race to the proportion of the Massachusetts population by race.  Asian, Black non-Hispanic, and Hispanic residents were overrepresented in the confirmed H1N1 cases; that is, the rate of H1N1 cases for this group was higher than their proportion of the population.  Asians make up less than 5% of Massachusetts, but accounted for about 7% of H1N1 cases.  Black persons make up about 7% of Massachusetts, but accounted for about 19% of H1N1 cases.  Hispanic persons make up about 9% of Massachusetts, but accounted for around 21% of H1N1 cases.  In contrast, while White, non-Hispanic persons accounted for the majority (51%) of H1N1 cases, they make up over 80% of Massachusetts, so were affected by a disproportionately lower rate of H1N1.

Slide 12 Race/Ethnicity Among Hospitalized Individuals with 2009 Pandemic H1N1 Influenza Compared to the Massachusetts Population
April 1, 2009 to January 5, 2010
Racial and ethnic minorities were also over represented among those hospitalized with H1N1 infection in terms of their proportion of hospitalized patients. This slide compares the percentage of the 389 people hospitalized with H1N1 influenza cases by race to the proportion of the Massachusetts population by race.  Asians had the same rate of H1N1 hospitalization as their proportion of the Massachusetts population.  Black non-Hispanic and Hispanic residents were overrepresented in hospitalizations for H1N1 influenza.  Black persons make up about 7% of Massachusetts, but accounted for about 19% of H1N1 hospitalizations.  Hispanic persons make up about 9% of Massachusetts, but accounted for around 20% of H1N1 hospitalizations.  White, non-Hispanic persons make up 80% of Massachusetts, but only accounted for around 56% of H1N1 hospitalizations.

Slide 13 Race/Ethnicity Among Individuals Who Died with 2009 Pandemic H1N1 Influenza Compared to the Massachusetts Population
April 1, 2009 to January 5, 2010
This slide compares the percentage of the 30 people who died with H1N1 influenza cases by race to the proportion of the Massachusetts population by race.  Asians had a slightly lower rate of death with H1N1 than their proportion of the Massachusetts population.  Black persons make up about 7% of Massachusetts, but accounted for about 14% of H1N1 deaths.  Hispanic persons make up about 9% of Massachusetts, but accounted for around 14% of H1N1 deaths.  White, non-Hispanic persons make up 80% of Massachusetts, but only accounted for around 67% of H1N1 deaths.

Slide 14 Rates of Laboratory Confirmed Cases of 2009 Pandemic H1N1 Influenza by Race/Ethnicity
Massachusetts, April 1, 2009 to January 5, 2010
When the confirmed cases are analyzed by race/ethnicity according to their overall population, there are still alarming disparities in the rates of confirmed H1N1 influenza.  The rates of laboratory confirmed H1N1 influenza among Asian, Black and Hispanic residents are more than two to four times as high as those for white residents.  This slide shows the rates of laboratory confirmed cases of H1N1 influenza per 100,000 by race/ethnicity between April 2009 and January 2010.  The rate for the total population was about 30 per 100,000.  For Asians, the rate was about 32.  For Black, non-Hispanic people, the rate was about 71.  For Hispanic people, the rate was about 63.  For White, non-Hispanic people, the rate was about 15.

Slide 15 Rates of Hospitalization with Pandemic H1N1 Influenza by Race/Ethnicity, per 100,000 Population
Massachusetts, April 1, 2009 to January 5, 2010
Racial and ethnic minorities were also over represented among those hospitalized with H1N1 infection in terms of their rates of hospitalization.  This slide shows the H1N1 influenza hospitalization rate per 100,000 by race/ethnicity between April 2009 and January 2010.  The rate for the total population was about 6 per 100,000.  For Asians, the rate was about 4.5.  For Black, non-Hispanic people, the rate was about 14.  For Hispanic people, the rate was about 11.  For White, non-Hispanic people, the rate was about 3.  Racial and ethnic minorities who had H1N1 were also hospitalized at much higher rates than their White counterparts.  Hispanics were hospitalized over 3 times more often, and Blacks were hospitalized more than 4 times as often.  (Asians were 1.5 times higher.)

Slide 16 Estimated Death Rates with Pandemic H1N1 Influenza by Race/Ethnicity, per 100,000 Population
Massachusetts, April 1, 2009 to January 5, 2010
Even more disturbing is the difference in death rates.  Blacks had a death rate more than 3 times higher than their White counterparts, Asians more than 4 times higher, and Hispanics almost 6 times higher.  This slide shows the H1N1 influenza death rate per 100,000 by race/ethnicity between April 2009 and January 2010, given 31 deaths from H1N1.  The rate for the total population was about 0.8 per 100,000.  For Asians, the rate was about 4.3.  For Black, non-Hispanic people, the rate was about 2.4.  For Hispanic people, the rate was about 4.2.  For White, non-Hispanic people, the rate was about 0.5.

Slide 17 Rate of Hospitalization with Pandemic H1N1 Influenza by Race/Ethnicity, by Age, per 100,000 Population
Massachusetts, April 1, 2009 to January 5, 2010
This slide shows the H1N1 influenza hospitalization rate per 100,000 by race/ethnicity, by age between April 2009 and January 2010.  The highest rates were for Hispanic children between 0 and 4 years (37 per 100,000); Black, non-Hispanic children between 0 and 4 (35 per 100,000); and Black, non-Hispanic youth between 5 and 24 years (22 per 100,000).  The lowest rates were for Asians between 25 and 49; White, non-Hispanic people age 65 and older; and White, non-Hispanic people between 25 and 49 (all less than 3 per 100,000).  Of those over 50 years, only Hispanic people had a rate above 10 per 100,000, with 13 per 100,000 for those between 50 and 64, and 15 per 100,000 for those 65 and older.

Slide 18 Proportions of Individuals Hospitalized in Massachusetts with 2009 Pandemic H1N1 Influenza, by Race/Ethnicity and Unreported Race/Ethnicity, Over Three Overlapping Time Periods
This slide shows the proportion of those hospitalized for H1N1 influenza by race/ethnicity during the periods of April 2009 to October 2009, October 2009 to December 2009, and overall.  During the period of April 2009 to October 2009, Asian, Hispanic, and Black, non-Hispanic people each made up a much larger proportion of those H1N1 hospitalizations.  During the next period from October to December, these three groups made up substantially smaller proportions of H1N1 hospitalizations.

Slide 19 Epidemiology/Surveillance
Proportion of Adults Immune from Natural Infection and Proportion with Natural and Vaccine Induced Immunity by State 
December 13, 2009
This slide compares adult immunity across the 50 U.S. states and District of Columbia.  Massachusetts, with an adult immunity rate of 50% (including both natural immunity and vaccine-induced immunity), has the 21st lowest rate in the country.  The lowest rate is Vermont, with an estimated 20% of adults immune.  The highest rate is Utah, with over 70% either naturally immune or vaccine-induced immune.

Slide 20 Epidemiology/Surveillance
Proportion of Adult Population Immune by Natural Infection and Vaccination
This slide shows a map of the U.S. with rates of adult population immunity.  Massachusetts is in the middle group of states by rate of immunity.