Decreasing Incidence of Pertussis in Massachusetts
Following the Introduction of Tdap
Noelle Cocoros, Nancy Harrington, Rosa Hernandez, Jennifer Myers, Linda Han, Susan Lett, Larry Madoff
Massachusetts Department of Public Health
Bureau of Infectious Disease Prevention, Response and Services
Results
Background
2000
2005: Tdap licensed
for ≥10 y/o
1500
Confirmed Pertussis Cases
Massachusetts 1904-2010
500
0
10
20
07
20
04
20
01
20
98
19
95
19
92
19
89
19
86
19
14000
Reported Cases
12000
10000
8000
1949: Pertussis
vaccine introduced
1967: Pertussis vaccine
2005: Tdap licensed
added to school
for ≥10 y/o
requirements
1996: Acellular pertussis
vaccine licensed
6000
4000
Pertussis Incidence by Age Group
160
0.60
140
0.50
infant
0.40
1-10
11-19
0.30
>20
0.20
0.080
4000
0.040
0.020
0.000
08
20
04
20
00
20
96
19
92
19
88
19
84
19
80
19
76
19
72
19
68
19
64
19
60
19
56
19
52
19
48
19
44
19
40
19
36
19
32
19
28
19
24
19
20
19
16
19
12
19
08
19
04
19
Bisgard KM, Pascual FB, Ehresmann HR, et al. Infant pertussis: Who was the Source? Pediatric Infectious Disease
Journal. 2004;23:985-9.
Edwards K. Overview of pertussis: Focus on epidemiology, sources of infection, and long term protection after infant
vaccination. Pediatric Infectious Disease Journal. 2005;24:S104-8.
Lee GM, LeBaron C, Murphy TV, et al. Pertussis in adolescents and adults: Should we vaccinate? Pediatrics.
2005;115:1675-84.
12000
0.3
10000
0.25
8000
0.2
6000
0.15
number positive
total tested
2003 2004 2005 2006 2007 2008 2009 2010
References
•The recent decline in the incidence of pertussis in infants
has occurred with the simultaneous decline in incidence
among adolescents. Our data show that adolescent and
infant incidence rates of pertussis track closely.
Pertussis serology results, HSLI
0.100
0
We calculated the incidence of confirmed pertussis cases from 2000 through 2010 in Massachusetts. We also evaluated
the age distribution of cases during these years. A confirmed case must meet one of the following criteria: (1) culture
confirmed, (2) serology positive at HSLI with at least 14 days of cough, (3) PCR positive with at least 14 days of cough
plus an additional symptom (whoop, paroxysms, or post-tussive vomiting), or (4) meets clinical case definition in criterion
3 and is epi-linked to a lab-confirmed case. Population estimates were obtained from the US Census. Tdap vaccination
rates in 7th graders are captured by our annual survey of school nurses. Laboratory data were obtained from the HSLI.
•The highest recent annual incidence of pertussis was in
2004, with an incidence of approximately 27 cases per
100,000. There were 12, 6, and 4 cases per 100,000 in
2008, 2009, and 2010, respectively.
Pertussis culture results, HSLI
1000
Methods
40
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
•Our annual school immunization surveys show that at
least 78% of 7th grade children (11-12 yr olds) in MA
received a dose of Tdap in 2009.
3000
20+ yr
total
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
0.060
11-19 yr
60
0
5000
1-10 yr
80
0.00
6000
<1 yr
100
20
2000
Year
120
0.10
2000
0
incidence per 100,000
0.70
•Since 2007, we have seen a substantial change in the
distribution of pertussis by age. Adults aged 20 years
and older now make up a large proportion of the total
cases while the proportion of cases among 11-19 year
olds has significantly declined.
1000
16000
Age Distribution of Pertussis Cases
proportion
The Massachusetts Department of Public Health (MDPH) has conducted enhanced Bordetella pertussis (pertussis) surveillance
since the early 1990s. Since then, every laboratory-confirmed case has been investigated by an MDPH epidemiologist or an
MDPH trained local board of health nurse. The Hinton State Laboratory Institute (HSLI) is the only state laboratory in the United
States that produces pertussis serology test results that are recognized by the Centers for Disease Control and Prevention
(CDC), allowing MDPH to capture cases with longer cough durations compared to PCR and culture testing alone. MDPH began
providing tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis vaccine (Tdap) universally for adolescents in the fall of
2005. There have been reports of increasing pertussis incidence in cities and states across the US in 2010 and early 2011, but
this trend is not evident in Massachusetts. We hypothesize that the decrease in pertussis incidence is due to adolescent
vaccination with Tdap, as demonstrated by the changing age distribution of cases.
percent positive
number positive
total tested
percent positive
4000
0.1
2000
0.05
0
0
2003
2004
2005
2006
2007
2008
2009
2010
The data from our state laboratory are presented above. The percent positive serology data for the last eight years correlate well
with our case counts for those years. However, the culture results are less consistent. (PCR testing was performed by HSLI from
Jan. 2005 through Oct. 2008; data are not presented.)
Conclusions
Pertussis incidence in Massachusetts has substantially declined in recent years, coinciding with the introduction of Tdap vaccine in 2
There have been no significant changes to our enhanced surveillance methodology. Further, the change in the age of pertussis cases