2017-2018 influenza season, boston - boston public health ... › healthdata ›...

2017-2018 Influenza Season, Boston

Communicable Disease Control Division

Infectious Disease Bureau

Boston Public Health Commission

Boston Public Health CommissionCommunicable Disease Control Division

Influenza Surveillance, Boston, 2017-2018

• The 2017-2018 influenza season

refers to the period between

10/1/2017-5/5/2018.

• Influenza cases diagnosed in Boston

and confirmed by any laboratory test

must be reported to the city health

department (Boston Public Health

Commission, [BPHC]).

SLIDE 1


Influenza Surveillance, Boston, 2017-2018

• BPHC syndromic surveillance data are used to

track influenza-like illness (ILI) visits at

Emergency Departments (EDs) in Boston.

• The %ILI represents the percent of all ED visits

attributed to ILI based on chief complaint data.

• During the season, data are used to inform

control measures and provide community and

stakeholder situational awareness.

• Data for this report were analyzed by BPHC at

the conclusion of the influenza season.

SLIDE 2


Reported Influenza Cases* and Percent of Emergency Department

Visits Due to Influenza-Like Illness (ILI)**, Boston, 2017-2018

Boston ED ILI data tracks well with laboratory-confirmed reports of influenza.

0%

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6%

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% IL

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Week Ending

Influenza Cases %ILI ED

SLIDE 3


Reported Influenza Cases by Influenza Type,

Boston Residents, 2017-2018

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Influenza A Cases Influenza B Cases

SLIDE 4

The proportion of total cases due to influenza B increases as the season progresses. This does not constitute a second wave

of influenza, but rather is consistent with what typically occurs during most influenza seasons.


Percent of Emergency Department Visits* for Influenza-like Illness (ILI), Boston, 2012-2018**

SLIDE 5

4.81%

5.23%

0%

1%

2%

3%

4%

5%

6%

Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug

% I

LI

/ A

ll V

isit

s

Month

2012-2013 2013-2014 2014-2015 2015-2016 2016-2017 2017-2018

*ED ILI visits: All visits to Boston Eds regardless of residence**Predominating influenza A subtypes by season:

2012-13: H3N2 (circulating virus was well matched to vaccine strain)2013-14: H1N1 (circulating virus was well matched to vaccine strain)2014-15: H3N2 (circulating virus demonstrated antigenic drift from vaccine strain)2015-16: H1N1 (circulating virus was well matched to vaccine strain)2016-17: H3N2 (circulating virus was well matched to vaccine strain)2017-18: H3N2 (circulating virus was well matched to vaccine strain)

While the 2017-2018 influenza season had a high percentage of ED ILI visits over a longer period than most prior seasons, the

2012-2013 season also had a relatively long period of increased ILI activity. During the first wave of the 2009 influenza A(H1N1)

pandemic (not shown here), Boston ED ILI peaked at 7.1%.


Characteristics of Reported Influenza Cases, Boston Residents, 2017-2018

Persons hospitalized with influenza had the highest mortality rate.

Total Cases N=4138

N (%)

Hospitalized 772 (19%)

Died (among total cases) 19 (0.5%)

Died (among hospitalized cases) 14 (1.8%)

N (%)

Influenza A * 3022 (73%)

Influenza B * 1115 (27%)

N (%)

Male 1778 (43%)

Female 2360 (57%) *Excludes one case who tested positive with a rapid diagnostic test that does not differentiate between flu types

SLIDE 6


Reported Influenza Cases, Boston Residents, 2017-2018

187

332

488

396

318

57

199

272

841

529

387

131

900 750 600 450 300 150 0 150 300 450 600 750 900

< 5

5-17

18-44

45-64

64-85

85+

Number of Cases

Age

Gro

up

(yr

s)

Female

Male

SLIDE 7

<5 yrs9%

5-17 yrs15%

18-44 yrs32%

45-64 yrs22%

65-84 yrs17%

85+ yrs5%

Distribution of Cases,

by Age Group and GenderDistribution of Cases, by Age Group

Persons 18 to 44 years of age accounted for the highest proportion of influenza cases.


Reported Influenza Cases by Age in Boston Residents,

Compared to the Overall Boston Population*, 2017-2018

9.3%

14.6%

32.1%

22.4%

17.0%

4.5%

5.2%

11.5%

52.7%

20.4%

8.6%

1.5%

0% 10% 20% 30% 40% 50% 60%

<5

5-17

18-44

45-64

65-84

85+

Percent of Total

Age

Gro

up

(yr

s)

% of Boston Population % of Reported Influenza Cases

Influenza disproportionately impacts extremes of age, specifically children less than 5 years of age, and persons 65 years

of age and older.

SLIDE 8


Reported Influenza Cases by Race/Ethnicity in Boston Residents,

Compared to the Overall Boston Population*, 2017-2018

5.2%

4.1%

7.0%

18.9%

33.0%

31.8%

4.6%

8.9%

17.5%

24.4%

53.9%

0% 10% 20% 30% 40% 50% 60%

Unknown

Other

Asian

Latino

Black

White

Percent of Total

Rac

e/E

thn

icit

y

Boston Population Reported Influenza Cases

Influenza disproportionately impacts Black residents, and to a lesser extent, Latino residents. This is consistent with data

BPHC has reported over the past several influenza seasons.

SLIDE 9


Influenza A vs. Influenza B Cases by Age Group,

Boston Residents, 2017-2018

Age Group (years)

<5 5-17 18-44 45-64 65-84 85+ Total

Influenza A 82% 72% 74% 71% 72% 66% 73%

Influenza B 18% 28% 26% 29% 28% 34% 27%

SLIDE 10

The overall distribution of influenza types by patient age was statistically significant (p=0.0005). Children less than 5 years of

age were more likely to be infected by influenza A compared with other age groups (p=0.0001). Persons greater than or equal to

85 years of age had a higher proportion of influenza B than other age groups (p=0.0249).


Characteristics of Reported Influenza Cases*, by Age Range,

Boston, 2017-2018

SLIDE 11

Persons greater than or equal to 45 years of age had higher hospitalization and mortality rates. No pediatric influenza

associated deaths were reported in Boston residents. The last pediatric influenza associated death in a Boston resident

occurred in 2012.

Age Group (years)

<5 5-17 18-44 45-64 65-84 85+ Overall

# Cases N=386 N=604 N=1329 N=926 N=705 N=188 N=4138

GenderMale (%) 48% 55% 37% 43% 45% 30% 43%

Female (%) 52% 45% 63% 57% 55% 70% 57%

White (%) 25% 16% 34% 33% 38% 55% 32%

Black (%) 34% 37% 29% 39% 33% 20% 33%

Race Latino (%) 16% 25% 20% 19% 17% 11% 19%

Asian (%) 10% 10% 6% 4% 8% 10% 7%

Other** (%) 6% 6% 6% 2% 2% 2% 4%

Hospitalized 8% 4% 7% 21% 42% 70% 19%

Died(N=0)

0% (N=0)

0% (N=0)

0%(N=4) 0.43%

(N=7) 1.00%

(N=8) 4.28%

(N=19) 0.46%

*Reported Cases: Boston Residents only.

**Other is inclusive of American Indian, Alaskan Native, Native Hawaiian, Pacific Islander, and unspecified “other” race.


Characteristics of Reported Influenza Cases* >64 Years of Age,

by Age Range, Boston, 2017-2018

*Reported cases: Boston Residents only.

**Race totals do not total 100% as those with unknown race are not shown

***Other is inclusive of American Indian, Alaskan Native, Native Hawaiian,

Pacific Islander, and unspecified “other” race

Case Demographics

Overall BostonPopulation

Case Demographics

Overall Boston Population

65-84 yrs 65-84 yrs 85+ yrs 85+ yrs

N=705 N/A N=188 N/A

GenderMale 45% 42% 30% 30%

Female 55% 58% 70% 70%

Race**

White 38% 55% 55% 68%

Black 33% 24% 20% 17%

Latino 17% 9% 11% 5%

Asian 8% 9% 10% 7%

Other*** 2% 3% 2% 2%

Hospitalized N/AN=294

42%N/A

N=132 70%

N/A

Died N/A(N=7)

N/A(N=8)

N/A1.00% 4.28%

SLIDE 12

Although racial and ethnic differences are noted in the 65 to 84 year old age group, disparities among Black and Latino residents

persist in persons 85 years of age and greater. Persons 85 years of age and greater were more frequently hospitalized with

increased mortality compared with persons between the ages of 65 and 84 years.


Hospitalization and Mortality Among Laboratory Confirmed Influenza

Cases* Evaluated at Acute Care Hospitals, 2014-2018

Over the past four influenza seasons, the 2017-2018 influenza season had the highest percent of ILI visits. However,

hospitalizations and mortality were highest during the 2014-2015 influenza season, which was also an influenza A(H3N2)

predominant season, though characterized by antigenic drift from vaccine strain.

**2014-15 2015-16 2016-17 2017-18

% Hospitalized 31.6% 20.9% 23.9% 24.8%

% Mortality 5.20% 4.80% 2.40% 1.80%

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osp

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*Boston residents only

Predominating influenza A subtypes by season:**2014-15: H3N2 (circulating virus demonstrated antigenic drift from vaccine strain)2015-16: H1N1 (circulating virus was well matched to vaccine strain)2016-17: H3N2 (circulating virus was well matched to vaccine strain)2017-18: H3N2 (circulating virus was well matched to vaccine strain)

SLIDE 13


Confirmed Influenza Cases and ILI Emergency Department (ED)

Visits in Boston Residents, 2017-2018

Confirmed Influenza Cases,

per 100,000 population, 10/1/2017-5/5/2018

ILI ED Visits,

per 100,000 population, 10/1/2017-5/5/2018

Neighborhood

Legend

A/B=Allston/Brighton

BB=Back Bay

CH=Charlestown

DOR=Dorchester

EB=East Boston

FW=Fenway

HP=Hyde Park

JP=Jamaica Plain

MT=Mattapan

RS=Roslindale

RX=Roxbury

SB=South Boston

SE=South End

WR=West Roxbury

SLIDE 14


Comparison of ILI Using Flu Near You (FNY)* and Boston Emergency Department (ED)

Syndromic** Data, 2016-2018

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Week Ending

Comparison of Flu Near You (FNY) ILI Data and ED Visits for ILI (2016-2018)

Metro Boston FNY % ILI % ILI ED Visits (Boston Hospitals)

↑ start of 2016-2017

influenza season

↑ start of 2017-2018

influenza season

*Flu Near You (FNY) compiles weekly data of ILI activity across the United States. The data come from short, weekly internet-based surveys completed by voluntary participants who indicate whether

they are healthy or have experienced any of a short list of symptoms; the FNY data represented are for the Boston metropolitan area***.**All visits to Boston EDs regardless of residence*** Boston metropolitan area: urbanized area around Boston as defined by the US Census Bureau; approximates towns and cities within the Route 128 belt.

SLIDE 15

Crowd source data (FNY) overall tracks well with ILI. However, the 2017-2018 influenza season’s extreme peak in Boston ED ILI percent

was not well reflected in FNY data. Factors such as aging populations and public perceptions of severity likely impacted reporting to

FNY.

The public may participate by enrolling in FNY at: https://flunearyou.org/

https://flunearyou.org/

Communicable Disease Control Division

Infectious Disease Bureau

P: (617) 534-5611

F: (617) 534-5905

www.bphc.org/cdc

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