Running head: PERTUSSIS 1..

Understanding the Epidemiology of Pertussis

Jessie McCarty

Concordia University

PERTUSSIS 2.

Define the Problem

Pertussis, also known to the general public as whopping cough, is an infection caused by

bacteria. This bacterial infection is caused by Bordetella pertussis and leads to a harsh cough

with multiple possible complications. Bordetella pertussis can be highly contagious, especially

in children, and in some cases, infection from pertussis can be fatal (Hockenberry, 2003).

Pertussis can be prevented, and the number of cases drastically reduced, by immunizing

communities. Therefore, pertussis is a disease of great significance to public health departments

throughout the United States and globally.

Due to the rising number of cases of pertussis throughout the United States, public health

departments nationally are starting to recognize the seriousness of this epidemic. Since the

1980’s, documented pertussis cases have increased (CDC, 2012b). A high peak occurred in

2004, with 25, 827 cases reported and another peak started in 2010 with 27,550 cases (CDC,

2012b). The peak of 2010 started to gradually decline in 2011 nationally. It is also important to

note many cases of pertussis are not reported and therefore, the amount of national cases is

higher than what the actual data shows. March of Dimes (2012) stated “It is estimated that up to

3.3 million cases of pertussis occur each year in adults and adolescents”. This number suggests

the majority of cases are not even reported and the epidemic is much larger than what the data

shows. The chart below shows the gradual increase of pertussis rates since 1980 and the peak in

2004 (CDC, 2012b).

PERTUSSIS 3.

(CDC, 2012b)

Pertussis can be a serious disease which can lead to serious complications and even

death. Bordetella pertussis is a preventable disease within a community when the public is

properly immunized. However, the number of people infected with pertussis on a yearly basis is

continuing to rise (Carmon & Spratling, 2010). According to March of Dimes (2012) “It's the

only vaccine-preventable disease that has been on the rise”. With the increased rates of pertussis

since the 1980’s, despite immunization availability, it is clear there are other factors contributing

to the increase of pertussis infections. Studying the epidemiology behind pertussis can lead to a

better understanding behind the growth of pertussis cases. In order to control and prevent

pertussis epidemics, public health departments must have an in-depth understanding of pertussis

and the multiple factors contributing to the epidemiology of this disease.

Describe the Agent

Bordetella pertussis is a gram-negative bacteria (CDC, 2012). This gram negative

bacteria produces many biologically and molecular responses. The presence of Bordetella

pertussis “produces multiple antigenic and biologically active products including pertussis toxin,

filamentous hemagglutinin (FHA), agglutinogens, adenylate cyclase, pertactin, and tracheal

cytotoxin” (CDC, 2012a). These responses to the gram negative Bordetella pertussis presence

then cause the signs and symptoms that present in the human infected with Bordetella pertussis.

PERTUSSIS 4.

The typical reservoir for Bordetella pertussis is a young child typically under the age of

five (McCance & Huether, 2006). Bordetella pertussis is a bacterium that typically affects young

children, specifically those who have not been immunized to pertussis (Hockenberry, 2003).

However, it is important to once again note Bordetella pertussis can affect adolescents and

adults.

After affecting one person, the pathogen finds its place of exit to go get transmitted

elsewhere. Pertussis is often transmitted via droplet transmission or contact transmission

(Hockenberry, 2003). Often, the pathogen is transmitted via a cough. The Bordetella pertussis

pathogen exits the infected person’s mouth by a cough and then is spread directly through the air

into another person’s airway. However, the pathogen can exit via a cough onto an object which

then transmits the bacteria via contact.

Once Bordetella pertussis is transmitted, it is able to enter the body of a new host by

droplet or contact transmission. The port of entry is typically the mouth. The droplets of the

pathogen can be inhaled by a new host via a cough. Also, not washing hands after touching

infected objects can also provide a way for contact transmission if people touch their faces with

contaminated hands. A susceptible host is often someone around the infected person. However,

those most susceptible are young children, those who are not vaccinated, and those with direct

exposure to others with Bordetella pertussis, such as family members.

Describe the Condition

The “incubation period for pertussis is most commonly seven to ten days, with a range of

four to twenty-one days” (Carmon & Spratling, 2010, p.239). The Bordetella pertussis

pathogen attaches “to the cilia of the respiratory epithelial cells, produce toxins that paralyze the

cilia, and cause inflammation of the respiratory tract, which interferes with the clearing of

PERTUSSIS 5.

pulmonary secretions” (CDC, 2012). This process of infection causes the signs and symptoms

related to pertussis. These signs and symptoms include “severe coughing, whooping, and post-

tussive vomiting which can last for many weeks” (Carmon & Spratling, 2010, p.239).

Pertussis infections can typically be separated into three stages: catarrhal, paroxysmal,

and convalescent stages (Carmon & Spratling, 2010). The first stage, catarrhal stage, can mimic

the common cold with symptoms such as sneezing, low grade fever, rhinorrhea, and a minor

cough. However, next in the paroxysmal stage, coughing worsens and a whooping noise is often

heard after a cough (Rittle, 2010). Also, it is important to note other symptoms, such as fever,

cyanosis, and post-tussive emesis, may also be present during this stage, especially with young

infants (Carmon & Spratling, 2010). Carmon & Spratling (2010) noted this stage “can last up to

ten weeks, with a typical duration of one to six weeks” (p.239). After the completion of the

second stage, the third and final stage, convalescent stage then starts. This stage is typically two

to three weeks but may last for months. Often, this stage consists of less severe symptoms and

the body recuperating.

Morbidity and Mortality Data

The World Health Organization (WHO) reported 139, 382 cases of pertussis globally for

2011 with 195,000 deaths worldwide (WHO, 2012). As aforementioned, there was a

documented peak in cases of pertussis in 2010 with the CDC reporting 27,550 cases and a

gradual decline in 2011 showing 18,719 (CDC, 2012a). The CDC (2012a) stated “Provisional

counts from our surveillance system indicate that more than 41,000 cases of pertussis were

reported to CDC during 2012”. If these numbers prove true, this would mean the United States

saw another peak of pertussis, higher than the peaks in 2004 and 20012. The chart below shows

rates of pertussis cases annually from 2000-2011 (CDC, 2012a).

PERTUSSIS 6.

Year Reported Cases*2000 7,8672001 7,5802002 9,7712003 11,6472004 25,8272005 25,6162006 15,6322007 10,4542008 13,2782009 16,8582010 27,5502011* 18,719

*Total reported cases include those with unknown age.(CDC, 2012a)

Data in the United States shows, after the peak of cases in 2004, 111 deaths related to

pertussis were documented between 2004 and 2008 (CDC, 2012b). In 2010, there were 27

deaths from pertussis (CDC, 2012a). CDC (2012a) stated “18 pertussis-related deaths during

2012 have been reported to CDC as of January 5, 2013. The majority of deaths continue to occur

among infants younger than 3 months of age”. Looking at data on morbidity and mortality for

pertussis, it is clear to see infants and young children are not only most likely to get this disease,

but also most likely to die from pertussis. March of Dimes (2012) even stated “92% of deaths

from pertussis occur in babies under 4 months of age”. In 2010, within the United States, there

were more than 18 documented deaths of infants from pertussis (March of Dimes, 2012). The

below chart further emphasizes the dangers of pertussis for infants.

PERTUSSIS 7.

Age at onset <3 mos >3 mos Total2004 23 4 272005 32 7 392006 12 5 162007 9 2 112008 16 2 18Total 92

(83%)20(17%)

111

Pertussis Deaths in the United States, 2004-2008(CDC, 2012b)

Host Characteristics

Age

Pertussis is a preventable disease with a known vaccine. However, pertussis still

continues to affect multiple children, adolescents, and adults every year. Cases of pertussis are

usually found in children, typically at the age of four and under (Hockenberry, 2003). CDC

(2012b) stated “The incidence rate of pertussis among infants exceeds that of all other age

groups. The second highest rates of disease are observed among children 7 through 10 years

old”. Many cases of pertussis reported in children and infants are reported in those who have not

received the immunization for Bordetella pertussis or have decreased immune function. Carmon

& Spratling (2010) even stated “the number of reported cases of pertussis has steadily increased,

particularly among the infant and adolescent age groups” (p.239). CDC (2012b) also

emphasized the importance of immunizing infants and children by stating “During 2001–2003,

the highest average annual pertussis incidence was among infants younger than 1 year of age

(55.2 cases per 100,000 population), and particularly among children younger than 6 months of

age (98.2 per 100,000 population). In 2002, 24% of all reported cases were in this age group”.

These statistics further stress the importance of immunizing infants as soon as possible.

PERTUSSIS 8.

Although cases of pertussis are usually talked about in reference to young children,

pertussis can affect adolescents and adults also. The increased infection rates in adolescents and

adults are believed to be correlated to eventually no longer having immunity from vaccinations

given in childhood (SuMi, HyunSoo, OkKyung, Moon-Hyun,& WhaSook, 2010). Also,

adolescents and adults with pertussis typically have more mild symptoms and the bacterial

infection is not as severe (Crose, Cruz, & Tornabene, 2012). CDC (2012b) stated “adolescents

(11–18 years of age) and adults (19 years and older) have accounted for an increasing proportion

of cases. During 2001–2003, the annual incidence of pertussis among persons aged 10–19 years

increased from 5.5 per 100,000 in 2001, to 6.7 in 2002, and 10.9 in 2003. In 2004 and 2005,

approximately 60% of reported cases were among persons 11 years of age and older”. Hence,

there is an obvious growing trend of adolescents and adults getting pertussis. The graph below

further shows this trend (CDC, 2012b).

(CDC, 2012b)

Sex

Unlike many diseases, research has not found a clear gender discrepancy with pertussis.

There are small studies which suggest females have higher rates of pertussis but many of these

studies have been discredited by larger studies. The majority of peer-reviewed research does not

show a definitive link between gender and pertussis. Fishman et al. (2011) stated “There was no

PERTUSSIS 9.

clinically significant change in proportions tested…gender” (p. 4). Also, Cagney, Macintyre,

Mcintyre, Puech, & Giammanco (2006) stated “Despite the female predominance of pertussis

notifications in the period covered by the study, we found no significant gender-specific

differences” (p. 1215). Based on the lack of correlation between sex and pertussis through

research, public health workers must assume both sexes are at equal risk for pertussis.

Race and Ethnicity

Pertussis can affect anyone of any race. However, in the United States, Caucasians are

most at risk for getting pertussis. CDC (2005) stated “Data on race was available for 24,024

(83%) persons with pertussis. Of these, 21,597 (90%) were white, 1,621 (7%) were black, 288

(1%) were American Indian/Alaska Native, 337 (1%) were Asian/Pacific Islander, and 181 (1%)

were identified as "other race”. This data proves a correlation between Caucasians and pertussis

infections. CDC (2005) further emphasized this racial correlation by stating “Among all age

groups, the incidence of reported cases was twice as high among whites as among blacks”.

A correlation between Hispanic ethnicity and pertussis should also be noted. CDC

(2005) explained “Data on Hispanic ethnicity was available for 23,669 (82%) persons with

pertussis. Of these, 3,871 (16%) were Hispanic. Among infants aged <6 months, 1,701 (29%) of

5,872 with pertussis were Hispanic; by comparison, an estimated 18% of infants born each year

in the United States are Hispanic”. This data suggests a strong link between pertussis and

Hispanic ethnicity, especially in the infant age group.

Environmental Attributes

Geographical Areas

Anyone living in the United States is at risk for pertussis, especially if not immunized.

However, there are certain areas throughout the United States which have seen more cases of

PERTUSSIS 10.

pertussis than others. For example, in 2012, the state with the most reported cases of pertussis

was Wisconsin followed by Minnesota, Vermont, and Washington (CDC, 2012a).

Many states have declared pertussis epidemics in 2012, including Wisconsin. According

to Wisconsin Department of Health Services (WDHS, 2013) “As of January 14, 2013, 6,189

cases (4,502 confirmed and 1,687 probable) of pertussis with illness onsets during 2012 have

been reported among Wisconsin residents”. The WDHS (2013) goes on to state “The recent

reported pertussis activity is the most observed since the large pertussis outbreak that occurred

during 2004-05. More than 5,600 reported cases occurred during 2004”. As aforementioned,

much of the data nationally from 2012 is showing higher numbers of pertussis cases than in the

last peak of 2004.

Although certain states may report higher cases of pertussis, it is important to keep in

mind certain states also have more organized systems of reporting infectious diseases than

others. Also, many cases of pertussis are not reported, or even diagnosed, especially in rural

areas. The below graphs and pictures help summarize which states have the highest pertussis

incidences.

States with incidence of pertussis the same or higher than the national incidence (as of November 23, 2012), which is 11.6/100,000 personsWisconsin 93.4 New Mexico 31.0 Arizona 13.5Minnesota 78.1* Alaska 28.6 Illinois 13.5Vermont 66.1 North Dakota 25.6 Idaho 13.1Washington 64.3 Oregon 22.1 Pennsylvania 12.9Iowa 47.5 Kansas 21.9 Missouri 12.3Maine 45.6 New Hampshire 15.7 - -Montana 44.3 Colorado 15.2 - -Utah 40.9 New York 14.5 - -

(CDC, 2012a)

PERTUSSIS 11.

(March of Dimes, 2012)

Social and Economic Factors

There are social and economic factors to take into account when studying pertussis.

Those exposed to smoke in their environment may be more susceptible to pertussis (Saadi et al.,

1996). This susceptibility is especially true for infants. Research has shown infants’ immune

responses to pertussis are slower when they are exposed to environments with smoke present

(Saadi et al., 1996).

Close living quarters is another social factor linked to a higher number of cases of

pertussis. A living situation where multiple people are present in a small area can enhance the

spread of pertussis. As aforementioned, pertussis can spread from close contact or by “indirect

contact with freshly contaminated articles” (Hockenberry, 2003, p. 656). Therefore, if pertussis

infects someone living in an environment with multiple people present, the disease can spread

easily to these other people. Those with a low income are more likely to live in this type of

living situation and public health departments must recognize this correlation.

PERTUSSIS 12.

Not only do those with a low income tend to live in housing situations which may make

them more susceptible for pertussis, but often those with low income often cannot afford

immunizations. Providing public programs for discounted or free vaccines is one way to make

sure children are vaccinated and adolescents and adults receive booster vaccines. Carmon &

Spratling (2010) explained “The pertussis vaccine is the most effective means for disease

prevention. The primary risk factor for pertussis is being unprotected or inadequately protected

from immunizations” (p. 241). Therefore, providing affordable vaccines is a reliable way to

encourage vaccinations, slow down the spread of the disease, and decrease the correlation

between low income and high risk for pertussis.

Occupation

There is no definitive correlation between occupation and pertussis cases. However,

those working in healthcare with exposure to pertussis are at a greater risk for pertussis due to

pertussis being highly contagious. Health care works can decrease their risk by quickly

recognizing the symptoms of pertussis and properly placing patients in isolation. Use of masks

and gowns is recommended in healthcare settings when interacting with patients with pertussis

symptoms.

Also, those working with small children, such as daycare workers and school teachers,

are at higher risk for pertussis infection since children are more likely to be infected with

pertussis. If children are infected with pertussis, they should not be attending school or day care

until cleared by a doctor to limit the spread of the infection.

Education

Although there is no clear link between a certain education level and pertussis infections,

general education about the disease will help decrease the spread of pertussis. Those in public

PERTUSSIS 13.

health must first make certain the public knows pertussis is a serious disease which can have

severe complications. Often, the public does not understand what pertussis is and who is

vulnerable to pertussis. Also, people assume they have had a vaccination once as a child and are

protected. Therefore, people do not feel vulnerable to the disease. Rittle (2010) stated “Many

adults think that pertussis is a thing of the past” (p.283). By educating the public about the

seriousness of pertussis and the continuation of the spread of pertussis, the public will understand

they are vulnerable to the disease and there is a threat. Education must also be provided to the

public on the effectiveness of the pertussis vaccine. By showing the vaccine works, and by

eliminating obstacles to getting the vaccine, the public will be more likely to get immunized.

Temporal Variation

Secular

According to the CDC (2012b) “Before the availability of a vaccine, pertussis was a

common cause of morbidity and mortality among children. During the 6-year period from 1940

through 1945, more than 1 million cases of pertussis were reported”. Vaccine introduction in

1940s helped to decrease the rates of pertussis and there were fewer than 5,000 annual cases in

1970 (CDC, 2012b). However, as mentioned earlier, in the 1980’s pertussis cases began to

increase and continue to grow. The below chart shows the secular trend in Pertussis from 1940-

2009 (CDC, 2012b).

PERTUSSIS 14.

(CDC, 2012b) Cyclic

Cherry (2005) stated “In the prevaccine era pertussis epidemics followed a cyclic pattern,

with peaks every 2 to 5 years” (p.1422). .  Unlike some diseases which occur in cycles and can

be predicted, pertussis has just been on a steady incline, with occasional peaks, since the 1980s

(CDC, 2012a). However, as noted by peaks in 2004, 2010, and the new numbers showing a

peak in 2012, one could infer the disease is following a cyclic pattern again. Cherry (2005)

explained “With the marked reduction of pertussis by vaccination, the same cyclic pattern still

occurs” (p.1422). Although not all researches agree pertussis is becoming cyclic, with trending

of peaks in the last 8 years, it is reasonable to suggest.

Seasonal

Pertussis can infect people at any time. However, the highest rates of pertussis in the

United States have been linked to the spring and summer months (Hockenberry, 2003). On the

contrary, CDC (2012b) reported “Pertussis has no distinct seasonal pattern, but it may increase in

the summer and fall”. This link between these seasons and pertussis has been noted throughout

the United States, although there is not a definitive cause as to why there is a correlation.

Epidemic

As aforementioned, pertussis cases have increased since 1980’s and there have been

peaks in 2004, 2010, and 2012. All of these peaks show an increase in cases of pertussis and

PERTUSSIS 15.

epidemics in the United States. Pertussis is a highly contagious disease and thus, even after

epidemics, the disease has a gradual decline in the next years and not a rapid decrease in the

disease. In 2012, many states declared epidemics of pertussis including Washington, Vermont,

and Wisconsin (CDC, 2012a). The below map shows the variation of the number of documented

cases of pertussis throughout the United States (CDC, 2012a). Many of the dark purple states

shown have had recent epidemics.

(CDC, 2012a)

Hypotheses Explaining Observed Distribution

As pertussis rates have increased since the 1980’s, people have speculated why there is

an increasing trend despite the availability of a vaccine. The introduction of a vaccine initially

proved to drastically slow down the spread of pertussis. CDC (2012b) stated “Following

introduction of whole-cell pertussis vaccine in the 1940s, pertussis incidence gradually declined,

reaching 15,000 reported cases in 1960 (approximately 8 per 100,000 population). By 1970,

annual incidence was fewer than 5,000 cases per year, and during 1980–1990, an average of

2,900 cases per year were reported”. However, in the 1980’s the rates of pertussis increased and

have never decreased to the numbers seen in the 1970’s. The below graph shows the drastic

decrease of pertussis rates after introduction of the vaccine.

PERTUSSIS 16.

(CDC, 2012b)

Some people believe pertussis rates are inaccurate due to the increased reporting, mainly

stemming from mandatory reporting in many states. Reporting of pertussis has not always been

mandatory and testing to confirm pertussis was not always available. Therefore, some argue

pertussis rates have not actually increased, but instead, the diagnosing and reporting availability

have simply increased.

The CDC also recognizes the correlation between increased reporting and rates. The

CDC (2012a) stated “Increased recognition and diagnosis of pertussis in older age groups

probably contributed to this increase of reported cases among adolescents and adults”.

However, diagnosis in younger children and infants has been prevalent for years and still shows

a rising rate. Therefore, there must be more behind the increasing rates than just the easier

ability to report data.

There are people who believe the pertussis vaccine is not helpful in protecting the public

from pertussis. However, scientific research has shown the vaccine does work in preventing

pertussis if given correctly and boosters are given. Cherry (2005) explained “data presently

exists that suggest that vaccine-induced immunity is actually better than induced by pertussis

infection” (p.1426). Therefore, vaccines do provide immunity to those who receive the vaccine.

PERTUSSIS 17.

However, it is important to emphasize the need to correctly follow the time frame for pertussis

shots and boosters.

Scientific data has also been collected showing the pertussis vaccine losing its protective

strength overtime, suggesting a need for booster shots. Rittle (2010) stated “the most dramatic

increase in pertussis incidence has been among adolescents and young adults and indicated that

this was due to the effects of waning of vaccine-induced immunity effectiveness” (p. 285).

Public Broadcasting Service (PBS, 2012) even stated “A full 92 percent of adults are no longer

inoculated against the disease — in large part because most Americans don’t know that a new

booster exists”. This statement further emphasizes the need for public education on the need for

booster shots. With 92% of adults not getting the correct booster shots, it is no wonder pertussis

remains an epidemic throughout many parts of the country. PBS (2012) further stated the

common vaccines given for pertussis, which are usually in combination with tetanus and

diphtheria vaccinations, “typically offer high levels of protection within the first two years of

getting vaccinated, but then protection decreases over time. This is known as waning immunity.

In general, DTaP vaccines are 80-90 percent effective. Our current estimate is that Tdap

vaccination protects 7 out of 10 people who receive it”. The need for booster shots, combined

with the waning immunity, would explain why cases of pertussis drastically decreased after the

introduction of the vaccine but then began to steadily increase again.

Gaps in Knowledge

Although there is not a clear cause for why pertussis cases are steadily increasing, much

research is showing there is an obvious link between lack of vaccinations and booster shots

leading to the spread of pertussis. Public education about the need for initial vaccinations, and

the need for booster shots, is necessary to slow the rate of pertussis.

PERTUSSIS 18.

Much more research is needed to understand the rising rates of pertussis. Further studies

into the vaccine itself are needed. PBS (2012) stated “Among kids who get all five doses of

DTaP on schedule, effectiveness is very high within the year following the fifth dose — at least 9

out of 10 kids are fully protected. There is a modest decrease in effectiveness in each following

year. About 7 out of 10 kids are fully protected five years after getting their last dose of DTaP

and the other 3 out of 10 kids are partially protected — protecting against serious disease”.

Perhaps further research into the vaccine will lead to a more effective vaccine throughout the

entire five years and decrease the need for frequent booster shots.

Further Epidemiological Research.

Overall, there is much research about the epidemiology behind pertussis. However, with

the growing rates of pertussis, it will be important to continue to research where pertussis cases

are increasing and what sexes, races, and ages are at most risk for pertussis. As increased

education is provided to the public, it will be interesting to see how public education about the

vaccine affects the number of pertussis cases. Also, with many states offering free pertussis

vaccines with hopes to slow down epidemics, epidemiological research will be needed to see

how free vaccinations affect the rates of pertussis.

Conclusion

Pertussis is a complex disease which can affect people of all ages. In order to stop the

spread of pertussis, public health departments must have not only an understanding of the

science behind pertussis, but also knowledge pertaining to all the factors involved with pertussis.

With the continued involvement of public health departments, and the cooperation of the public

to get properly immunized, there is hope that someday pertussis will be eradicated

PERTUSSIS 19.

References

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trends for nurses. Pediatric Nursing, 36(5), 239-243.

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PERTUSSIS 20.

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