H1N1 Influenza in Boston:Past, Present, and Future

Media BriefingBoston Public Health Commission

August 17, 2009

Age Distribution of CasesAs of July 31, 2009, 480 cases of confirmed novel H1N1 influenza have been identified in Boston.

Of the confirmed cases, 296 (62%) are under 18 years of age, with a median age of 13. 18% of cases are under age 5 and 91% are under age 45; only 41 cases (9%) have been over age 45.

Novel H1N1 Diagnosing Health Care Sites: April-July, 2009

Weekly incidence rates of H1N1 Influenza cases, by zipcodeApril 26 to June 6, 2009

Gender of Novel H1N1 Cases Compared to the Boston Population

Race/Ethnicity of Novel H1N1 Cases Compared to the Boston Population

Race/Ethnicity of Hospitalized Novel H1N1 Influenza Cases

Black 35 (49%)Hispanic 20 (28%)Other 5(7%)White 11 (15%)

Characteristics of 71 Hospitalized Novel H1N1 Boston Cases

Characteristic N (%)

Age Group 0-4 years 20 (28%)

5-17 years 22 (31%)

18-44 years 16 (23%)

45-64 years 8 (11%)

65+ years 5 (7%)

ICU Admission 26 (37%)

Asthma 35 (49%)

Pneumonia 26 (37%)

Respiratory Support CPAP/BIPAP 10 (14%)

Intubation 7 (10%)

Reported Influenza A* and Novel H1N1 Influenza by Neighborhood: April-July, 2009

*Estimated that the majority were H1N1Novel H1N1 = 477 cases; Influenza A = 508 cases

ED Visits for Influenza-like Illness (ILI)

Summary of Boston Emergency Department Visits

Time period (60 days) Total Visits* Visits for ILI** (% of all visits)

April 15 - June 14, 2009 94,915 3,907 (4.1%)

April 15 - June 14, 2008 85,122 652 (0.7%)

January 7 - March 8, 2009 84,904 1,688 (1.9%)(2009 influenza season)

*visits to 10 Boston emergency departments

**ILI defined as "flu" or "fever and a respiratory symptom", as described in the patient's chief complaint

The Boston Public Health Commission closely monitors emergency department visits for influenza-like illness (ILI) and other respiratory conditions.

From April 15 to June 14, 2009, total visits and visits for ILI increased significantly. During that period 4.1% of all visits were for ILI, compared with 0.7% during the same time period in 2008, and 1.9% during the peak of the 2009 seasonal influenza season, from January 7 to March 8, 2009.

Percent of Emergency Department Visits for Influenza-like Illness2009 vs. prior years

Estimated impact of H1N1 by neighborhood

Estimated

CasesPopulatio

n* % AffectedBoston, MA 23,388 589,230 4.0%

Overall neighborhood estimates, by percent affected

Above Citywide average (>4.3%) Est. Cases Population % AffectedEast Boston 3,082 38,413 8.0%

Roxbury 2,077 34,665 6.0%Fenway 2,698 47,449 5.7%

Allston/Brighton 3,296 66,467 5.0%North Dorchester 3,018 58,675 5.1%South Dorchester 3,444 75,329 4.6%

Mattapan 1,226 27,815 4.4%Total, neighborhoods with high activity 18,841 348,813 5.4%

Below Citywide average (<4.3%) Hyde Park 1,029 28,392 3.6%Roslindale 1,168 32,527 3.6%

Charlestown 420 15,195 2.8%South Boston 542 30,048 1.8%

South End 397 27,311 1.5%Jamaica Plain 329 36,293 0.9%

Back Bay/Beacon Hill/West End/North End/Downtown 232 46,258 0.5%

West Roxbury 169 24,058 0.7%Total, neighborhoods with low activity 4,286 240,082 1.8%

School ClosingsHigh, sustained rates of absenteeism caused by influenza-like illness led to temporary school closures in certain instances.

School closures were recommended on a case by case basis, and lasted an average of 7 days.

Burden of H1N1 Influenza Activity: School Assessment Findings

Compared to schools that remained open, closed schools:– experienced greater burden of H1N1 influenza activity, as

measured by staff out sick and students sent home sick – were more likely to report difficulty keeping ill students

out of school (44% vs. 27%)

Percent Attendance in Closed Boston Public Schools

School February Baseline Pre-Closure* Post-Closure*

A 95 78 87

B 96 89 96

C 94 88 88

D 91 77 90

E 94 88 90

F 93 77 90

G 95 78 93

H 95 69 89

I 95 69 83

J 95 79 94

K 92 84 86