PERTUSSIS 1.
Understanding the Epidemiology of Pertussis
Jessie McCarty
Concordia University
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).
(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, adenylatecyclase, 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.
The typical reservoir for Bordetella pertussis is a young child typically under the age of five (McCanceHuether, 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 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).
Year / Reported Cases*2000 / 7,867
2001 / 7,580
2002 / 9,771
2003 / 11,647
2004 / 25,827
2005 / 25,616
2006 / 15,632
2007 / 10,454
2008 / 13,278
2009 / 16,858
2010 / 27,550
2011* / 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.
Age at onset / <3 mos / 3 mos / Total2004 / 23 / 4 / 27
2005 / 32 / 7 / 39
2006 / 12 / 5 / 16
2007 / 9 / 2 / 11
2008 / 16 / 2 / 18
Total / 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.
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 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 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 onsetsduring 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 / 13.5
Minnesota / 78.1* / Alaska / 28.6 / Illinois / 13.5
Vermont / 66.1 / North Dakota / 25.6 / Idaho / 13.1
Washington / 64.3 / Oregon / 22.1 / Pennsylvania / 12.9
Iowa / 47.5 / Kansas / 21.9 / Missouri / 12.3
Maine / 45.6 / New Hampshire / 15.7 / - / -
Montana / 44.3 / Colorado / 15.2 / - / -
Utah / 40.9 / New York / 14.5 / - / -
(CDC, 2012a)
(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.
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 oftencannot 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 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).