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COURSE OBJECTIVE: The purpose of this course is to enable healthcare professionals to understand the significance in the rise of pertussis to epidemic levels and prepare them to provide appropriate preventive, assessment, diagnostic, and treatment services/methods for patients suffering from the disease.
Upon completion of this course, you will be able to:
Pertussis, commonly known as whooping cough, is a very contagious bacterial disease spread from person to person primarily through large droplets released into the air by coughing and sneezing. These droplets contain the pertussis-causing bacteria, which then enter the mouth or nose of another person. Pertussis is also known to be transmitted by handling tissues and other materials containing the droplets, which are then transmitted to the mouth or nose.
Pertussis results in severe coughing attacks, and the disease can last for months. It is a life-threatening disease for infants, who are too young to receive vaccinations against its risk. After a period of great decline, pertussis is currently on the rise again and has reached epidemic proportions in areas of the United States and other developed countries.
Grace is an 8-month-old infant, the youngest of three children. Developmentally, she has had a normal, healthy infancy, and thus far, she has received all of the immunizations recommended by the American Academy of Pediatrics. Maria, her mother, has had a minor “cold” for the past week, and when Grace wakes one morning with sniffles and a runny nose, she assumes that Grace has caught the same cold. Her siblings, however, have no symptoms.
After a week with a low-grade fever and a runny nose, Grace develops a mild, occasional cough, which increases over the next week. Maria notices that every now and then after coughing, Grace seems to stop breathing. Cautious but not overly concerned, Maria takes her daughter to the doctor expecting to be told that Grace has a common respiratory ailment. Maria never anticipates that both she and her daughter will be diagnosed with pertussis.
The cause of pertussis, or whooping cough, is a bacteria known as Bordetella pertussis (B. pertussis), a Gram-negative, aerobic coccobacillus. This bacteria produces a number of virulence factors, including pertussis toxin, adenylate cyclase toxin, filamentous hemagglutinin, and hemolysin. Humans are this bacterium’s only known reservoir.
Pertussis is a toxin-mediated respiratory disease. The disease-causing bacteria attach themselves to cilia in the upper respiratory system and then release toxins that paralyze the cilia and cause inflammation. This paralysis and inflammation interfere with the clearing of pulmonary secretions. In the past it was thought that this bacterium does not invade tissues, but studies have shown that it is also present in alveolar macrophages.
The pathogenesis of pertussis involves two stages:
Once a person has been exposed to pertussis bacteria, symptoms may develop within 7 to 10 days, but the disease can incubate for up to 6 weeks. The course of the disease follows three clinical stages, the first two of which parallel the organism’s pathogenesis (described above): catarrhal/colonization, paroxysmal/toxemic, and convalescent.
Pertussis most commonly affects children and infants, but adolescents and adults are also susceptible. Called the “cough of 100 days” by the Chinese, the disease can be fatal, particularly for infants under one year of age.
Pertussis presents as a milder disease in adolescents, adults, and children who are partially protected by the vaccine. These persons may present with a mild or persistent cough, without an inspiratory “whoop,” or they may be completely asymptomatic. Even though the disease may be milder in older persons, those who are infected may transmit the disease to other susceptible persons, including unimmunized or incompletely immunized infants. An older person in a household with multiple pertussis cases is often the first to acquire the disease and a source of infection for children in the home.
Pertussis is a public health issue, and cases—both probable and confirmed—must be reported to the Centers for Disease Control and Prevention (CDC) through the National Notifiable Diseases Surveillance System (NNDSS). Records of reported pertussis cases have been compiled since 1922.
Prior to the introduction of the pertussis vaccines (DTP) in the 1940s, reported cases of pertussis often exceeded 100,000 cases each year. By 1965, however, reported cases declined to fewer than 10,000. During the 1990s, pertussis cases began to rise, and by 2013 there were over 28,000 cases reported in the United States (CDC, 2014a). From January 1 to June 16, 2014, 9,964 cases of pertussis were reported by the 50 states and Washington, D.C. This was a 24% increase compared with the same period in 2013 (CDC, 2014b).
Infants less than one year old, who are at greatest risk for severe disease and death, continue to have the highest reported rate of pertussis, and school-aged children 7 to 10 years now comprise a large proportion of reported pertussis cases (CDC, 2014a).
|Source: CDC, 2014a.|
|Calculated from 24,135 cases with age reported.|
From 2013–2014, many states reported increases in pertussis cases compared to 2012–2013, and epidemics were reported in both California and Washington State.
While the reasons for the increase in cases of whooping cough are not fully understood, multiple factors are likely involved and may include:
Protection from pertussis vaccines given to children continues to be excellent during the first few years after vaccination but wears off over time. Outbreaks and epidemics in the United States are consistent with waning immunity seen as this protection diminishes.
It is suspected that this is due to the change in the 1990s from pertussis vaccines that used full-strength doses of the whole bacteria cell to reduced doses of acellular vaccines, which only contain parts of the bacteria. An FDA study using animals exposed to the pertussis bacterium showed that both types of vaccines provide excellent antibody responses, but those that received an acellular pertussis vaccine had the bacteria in their airways for up to six weeks and were able to spread the infection to others who were not vaccinated. In contrast, those that received the whole-cell vaccine had no bacteria present within three weeks (USFDA, 2013).
These findings suggest that even though individuals immunized with acellular pertussis vaccine may be protected from the disease, they might still become infected without becoming sick and are able to spread the infection to others (Parch, 2014).
“Vaccine refusers” are parents who choose not to have their children vaccinated because they believe vaccines are not safe. Among others, two major concerns parents have are that children are being given too many shots too soon and that there is a link between the preservative thimerosal and health problems such as autism. These concerns pose difficult challenges for healthcare professionals, and it is important to educate parents about the facts.
Scientific data show that receiving multiple vaccines has no harmful effect on a healthy child’s immune system, and there is no evidence of negative neuropsychological outcomes.
Thimerosal contains a form of mercury that was used in very small amounts since the 1930s. There is no evidence of harm caused by the very small amounts of thimerosal used in vaccines, but as a precautionary measure it has been removed from most all vaccines since 2001, with no decline in the rates of autism. The cause of autism is unknown, but the current theory is that it is a genetically based disorder that occurs before birth (AAP, 2013).
Vaccine refusal has been considered a significant factor in the rise of pertussis but has been shown to be questionable, in that during a recent outbreak in California, most of the children who contracted pertussis were immunized. It is known, however, that when more parents choose to delay or refuse recommended childhood vaccinations, the overall rate of vaccination drops, the population as a whole becomes less immune to the disease, and more opportunities are created for whooping cough outbreaks (Parch, 2014).
The healthcare community has become more aware of the disease, its symptomatology, and its significance. As a result, there have been advances made in diagnostic testing and reporting. Laboratory diagnosis of pertussis has gone through many changes in the last 20 years, with continuing improvement in early detection. These changes have revealed the importance of pertussis in older persons and their role in disease transmission (Loeffelholz, 2012).
Many changes have also enhanced the completeness of reporting. These changes include the use of electronic laboratory reports, the searching of hospital and laboratory records, the use of administrative datasets (e.g., Medicare and Medicaid), and expanded sources of reporting beyond the physician (Roush, 2014).
A universal vaccine for children has been recommended since the mid-1940s and has made great inroads in the prevention of the disease. Maintaining a high rate of vaccination among infants, children, adolescents, and adults is considered the most effective way to prevent pertussis.
There are two types of pertussis vaccines currently available:
To reduce the number of shots that a person receives at one office visit, pertussis vaccines are given in combination with diphtheria (D or d) and tetanus (T) vaccines. The uppercase letters refer to full-strength and lowercase to reduced-strength doses.
In the United States full-strength diphtheria and tetanus and reduced-strength pertussis (DTaP) vaccine is given to children under 7 years of age. Full-strength tetanus and reduced-strength diphtheria and pertussis (Tdap) is given to older children and adults (CDC, 2013b).
The American Academy of Pediatrics (2014) states that children younger than 7 years of age should get five doses of DTaP, one dose at each of the following ages: 2 months, 4 months, 6 months, 15 to 18 months, and 4 to 6 years.
Children 7 to 10 years old who were not fully immunized should receive the Tdap booster shot, which is also recommended for adolescents 11 to 18 years of age and adults 19 to 64. Updated recommendations now state that Tdap should be given to all adults 65 years and older (CDC, 2012).
Because vaccination provides immunity to an unborn child, pregnant women should receive a dose of Tdap between 27 and 36 weeks gestation during each pregnancy, irrespective of their prior history of receiving Tdap, as studies have shown that when the source of pertussis was identified, mothers were responsible for 30% to 40% of infant infections (CDC, 2014c).
Because approximately 80% of cases have been shown to be caused by someone in the home, the CDC (2014d) recommends encouraging persons in close contact with infants to be up to date with their pertussis vaccine.
“Cocooning” involves vaccination of the mother during pregnancy, as recommended, and vaccination of other family members and caregivers. This might include daycare facility workers, nannies, teenage babysitters, and healthcare professionals. Cocooning is important, but it is impossible to make certain that everyone around an infant has been vaccinated. The CDC suggests that cocooning might not be enough to prevent pertussis illness and death in infants, but it does provide them with some indirect protection.
Because of the increased exposure healthcare workers face, they are at greater risk of contracting pertussis. Pertussis outbreaks in the workplace are not only stressful for the individual, but they can be costly and disruptive for the place of employment. To help counterbalance the increased risk for healthcare workers, the CDC recommends that all employees with direct patient contact receive a Tdap booster every 10 years or more often.
Pertussis is spread through airborne droplets expelled during coughing or sneezing. These droplets are known to travel a distance of three feet. Transmission risk increases when a person is confined in close proximity to a symptomatic person for more than an hour.
Patients with suspected or confirmed pertussis should preferably be placed in a private room, and droplet precautions should remain in place until the patient has received five days of effective antimicrobial therapy.
In the healthcare setting, workers should wear a surgical mask when in contact with any coughing patient. They should wash their hands after any patient contact and after contact with inanimate objects within the patient’s room. If a healthcare worker or household contact was not wearing a mask and was within three feet of an infectious pertussis patient, preventive antibiotics are recommended (CDC, 2014e).
Precautions should be taken to prevent cross-contamination between sample collection and in the laboratory by wearing protective gloves, disinfecting surfaces with a low-level disinfectant, and washing hands thoroughly and regularly.
Routine cleaning and disinfecting is recommended to reduce the spread of pertussis. B. pertussis survival rates include:
Source: PHAC, 2010.
When using a disinfectant, concentration and contact time for each product will differ. Surfaces should be sprayed until completely wet and should remain wet for the length of time specified for the disinfectant (contact time). The surface should be resprayed if it dries before the recommended contact time.
Schools, work places, and other public settings bring persons into contact with others who may be infected with pertussis. Pertussis is quite contagious among contacts such as household members; persons who are face-to-face within three feet of each other for more than one hour; and persons who have direct contact with respiratory, oral, or nasal secretions.
Unfortunately, pertussis is most contagious before an infected person has any symptoms of the disease, making transmission even more likely. It is imperative that people, including children, be taught to practice healthy habits known to reduce risk of contagion. One of the most effective habits is to wash hands or use a hand sanitizer after:
Other healthy habits are to:
Persons with confirmed pertussis should be isolated at home until they have completed their course of antibiotics, usually 5 to 14 days depending on the antibiotic prescribed. Persons with suspected pertussis should also be isolated at home until negative PCR test results are available.
A child sent home from school with suspected pertussis will be excluded from school for at least 21 days or until coughing is completely resolved. Any student with confirmed pertussis who is not treated will be excluded from school for that length of time also. This applies to daycare centers as well (LADPH, 2014).
When a patient comes into the office with common respiratory complaints, the clinician should first conduct an interview to ascertain the symptoms being experienced, their time of onset, and the duration and severity of the illness. During this interview, the patient’s personal history and family health history should also be solicited. Next, a physical examination is performed, vital signs are recorded, and observations made about the patient’s appearance and activity. Specifically, clinicians will check for coughing (with or without a whoop), nasal congestion, apnea (in infants), fatigue, and a low-grade fever as potential signs of pertussis.
If enough evidence exists to suggest that pertussis may be present, then diagnostic tests are recommended. There are three main diagnostic tests for pertussis: culture, polymerase chain reaction (PCR), and serology.
Depending on when a patient visits the doctor’s office, different tests are more effective; within the first two weeks—when viable bacteria levels are highest—a culture or PCR provides the most accurate reading. However, many patients do not seek medical treatment until they are well into the paroxysmal stage of the illness, when coughing has become increasingly disruptive. From about three weeks on, serology is the most accurate diagnostic tool.
Source: CDC, 2013c.
For both PCR and cultures of suspected pertussis cases, a nasopharyngeal (NP) swab or aspirate must be obtained. According to the CDC (2013d), once an NP swab has been collected, it should be plated directly or placed into transport medium immediately. NP aspirates should be dispensed and plated within 24 hours of collection. The same specimen can be used for both a culture and PCR. (See the figures below for examples of how to successfully obtain an NP swab or aspirate. See also “Resources” at the end of this course for a link to a video demonstrating proper NP techniques.)
Proper technique for obtaining a nasopharyngeal specimen for isolation of B. pertussis. (Source: CDC, 2013d.)
The CDC recommends a series of PCR best practices to avoid inaccurate diagnosis of pertussis specimens. Specifically, the following guidelines are suggested:
Source: CDC, 2013e.
At the doctor’s office, the nurse, Kathy, interviews Maria and finds that Grace’s symptoms have been present for the past two weeks, mild at first but increasing in severity with recent episodes in which she appears to stop breathing. The fact that Grace has been suffering from apnea immediately arouses Kathy’s suspicion that this illness is more than a common cold.
Noting that Maria is also sniffling, Kathy conducts a recent family health history and learns that Maria herself has been experiencing respiratory infection symptoms for the past seven days. Because she knows that previously immunized adults may manifest only mild symptoms of pertussis, and because she understands that waning immunity in adults can lead to the accidental spread of the disease, Kathy suspects that Maria’s illness may be connected to Grace’s apnea.
Kathy reports her findings to the physician, and following physical examination, it is recommended that both mother and daughter undergo diagnostic testing for pertussis. Nasopharyngeal specimens are obtained from both and sent for PCR testing and culture.
Pertussis is a nationally notifiable disease, and as such, clinical cases must be reported to local health departments. Tracking pertussis can help prevent its spread while also revealing patterns about how, when, and where the disease is manifesting itself. Both probable and confirmed cases should be reported.
To clarify the distinction between probable and confirmed, the CDC provides a clinical case definition that is crucial for healthcare professionals to follow given the limitations of lab diagnostics and the underreporting of pertussis cases due to misdiagnosis.
|Source: CDC, 2014a.|
|Clinical case definition||In the absence of a more likely diagnosis, a cough illness lasting ≥2 weeks with one of the following symptoms:
|Probable case classification||
|Confirmed case classification||
The initial diagnosis of a patient with pertussis is based on the case assessment (oral interview and physical examination). However, because pertussis presents like other common respiratory infections for the first few weeks, and because some patients may be asymptomatic, it can be difficult to make an initial pertussis diagnosis. Moreover, many patients often wait to visit the doctor until the disease has already progressed to the second stage, when diagnostic tests are limited to serological assays.
Thus, the CDC (2013f) recommends that clinicians strongly consider treating prior to confirming test results if the clinical history is strongly suggestive or if a patient is at risk for severe or complicated disease (e.g., infants). Given the potential health risks associated with pertussis, its high degree of contagiousness, and the rise in incidence of the disease, treating suspected cases prior to receiving definitive results can be a responsible option for healthcare providers.
In some cases, there is little to prescribe beyond a regimen of rest, since pharmaceuticals are an effective treatment option for pertussis only if administered early on in the course of the disease. The decision to prescribe pharmaceuticals varies depending on the age of the patient, risk factors involved, severity of symptoms, how long a patient has already been ill, and so on. If drugs are prescribed, the macrolides azithromycin, clarithromycin, and erythromycin are the preferred treatment for persons at least 1 month of age.
The CDC presents specific recommendations for pharmacologic intervention:
Some negative side effects, including gastrointestinal ailments and rashes, may result from the use of macrolides. When choosing which drug to administer, clinicians should take into consideration its safety, effectiveness, cost, tolerability, and ease of regimen.
Infantile hypertrophic pyloric stenosis (IHPS) is a form of gastric outlet obstruction that occurs in about 3 in every 1,000 babies born in the United States. When an infant suffers from IHPS, the pylorus muscles of the stomach thicken abnormally and block the pyloric channel so that food is unable to leave the stomach and enter the small intestine. The condition can cause vomiting, dehydration, and fluid imbalances and must be surgically repaired. There is a causal link between use of erythromycin in the first 2 weeks of life and development of IHPS, so it should be avoided as a pertussis treatment in infants <1 month old.
Source: Cronan, 2011.
When a patient with pertussis is experiencing extreme breathing difficulties or other complications, hospitalization is recommended. Once admitted, patients may receive IV fluids to alleviate dehydration. Airway suctioning may be required, and an oxygen tent with high humidity or a ventilator is often used to assist with breathing. Prevention of secondary infections and attentive nursing care are important components of hospitalization.
Because Grace has had a cough illness lasting two weeks or longer with apnea, the primary care provider (PCP) determines that Grace meets the clinical definition of pertussis and that Maria may be the source of her illness.
Strongly suspecting that Grace and Maria will test positive for pertussis based on clinical history, their PCP starts both of them on a regimen of azithromycin, from which Grace develops gastrointestinal side effects. After a day on the medication, Grace, who is now suffering from both diarrhea and a more severe cough that keeps her from nursing effectively, becomes dehydrated. Maria, noting her daughter’s listlessness and inability to ingest liquids, calls their PCP, who advises her to take Grace to the hospital. Grace is admitted to the hospital, given IV fluids to alleviate her dehydration, and closely monitored for emergence of other complications.
For treating a child with pertussis at home, the CDC (2013g) recommends:
A 1:10 solution of household bleach includes 1 part bleach and 9 parts water. The key is using the same volume as a “part”—i.e., a measuring tablespoon or a measuring cup.
Source: CDC, 2009.
The CDC (2013) is actively promoting the judicious use of antibiotics among healthcare providers and parents and supports targeting postexposure prophylaxis (PEP) antibiotics to persons at high risk of developing severe pertussis and to persons who will have close contact with those at high risk of developing pertussis. It therefore recommends providing PEP to:
With excellent hospital care, Grace survives the complications brought on by her pertussis infection. After seven days of treatment in which she receives IV antibiotics as well as fluids to combat her dehydration, Grace is released from the hospital and returns home to her family. She still has a cough that will linger for several more weeks, and her parents watch closely to make sure that she doesn’t develop a secondary infection as indicated by a fever.
Meanwhile, Maria is still taking her own antibiotics, and her husband, Greg, has also been given a prophylactic prescription, since he hasn’t received a Tdap booster and will be coming into close contact with both infected family members. With rest, fluids, and time, both Grace and Maria gradually return to good health.
PCR results and cultures return positive for both Grace and Maria, and their primary care provider reports two confirmed cases of pertussis to the local health department.
As pertussis progresses, it may lead to related complications that can pose serious health risks. Life-threatening complications are most common in infants under 3 months of age. According to the CDC (2014f), hospitalization is most common in infants younger than 6 months of age.
Common complications for hospitalized infants include pneumonia, convulsions, apnea, encephalopathy (as a result of hypoxia from coughing or possibly from toxin), and death. For those infants who die from the disease, refractory pulmonary hypertension is common, and encephalopathy occurs in 20% of these cases.
Other complications can include anorexia, dehydration, difficulty sleeping, epistaxis, hernias, otitis media, urinary incontinence, pneumothorax, rectal prolapse, and subdural hematomas (CDC, 2014f).
For adolescents and adults, the kinds of complications stemming from pertussis tend to be more directly related to the physical effects of the cough, and less than 5% of patients require hospitalization. Common complications in those who do require hospital care are listed in the table below. Other complications can include anorexia, dehydration, epistaxis, hernias, and otitis media. More severe complications can include encephalopathy as a result of hypoxia from coughing or possibly from toxin, pneumothorax, rectal prolapse, subdural hematomas, and seizures (CDC, 2014f).
Other less common complications have been reported, including ulcers on the tongue and mouth, low blood pressure requiring medication, kidney failure requiring temporary dialysis, and damaged vocal cords (NHS, 2013).
Source: CDC, 2014f.
Pertussis, or whooping cough, has traditionally been seen as a childhood disease, but in fact, it is potentially dangerous for people of all ages. Infants are the most vulnerable to the illness and often develop related complications that require hospitalization and sometimes lead to death. Violent paroxysms of coughing and the extended duration of pertussis make it particularly challenging to endure, but if caught within the first few weeks of onset, the disease can be treated with antibiotics.
Waning immunity in adolescents and adults has challenged efforts to eradicate the disease, and the incidence of pertussis is currently on the rise among all age groups under 20 years of age, reaching epidemic proportions in some areas of the United States. Childhood vaccination and subsequent booster shots for adolescents and adults are the best method for combating the spread of this infectious disease.
Pertussis (including audio of “whooping”)
Parents of Kids with Infectious Diseases
Pyloric Stenosis (KidsHealth)
NOTE: Complete URLs for references retrieved from online sources are provided in the PDF of this course (view/download PDF from the menu at the top of this page).
American Academy of Pediatrics (AAP). (2013). Immunization resources: addressing common concerns of vaccine-hesitant parents. Retrieved from http://www2.aap.org
American Academy of Pediatrics (AAP). (2014). Immunization: 2013 immunization schedules. Retrieved from http://www2.aap.org
Centers for Disease Control and Prevention (CDC). (2014a). Pertussis (whooping cough): surveillance & reporting: trends. Retrieved from http://www.cdc.gov
Centers for Disease Control and Prevention (CDC). (2014b). Pertussis (whooping cough): pertussis outbreak trends. Retrieved from http://www.cdc.gov
Center for Disease Control and Prevention (CDC). (2014c). Tdap for pregnant women: information for providers. Retrieved from http:///www.cdc.gov
Centers for Disease Control and Prevention CDC). (2014d). Surround babies with protection. Retrieved from http://www.cdc.gov
Centers for Disease Control and Prevention (CDC) (2014e). Postexposure antimicrobial prophylaxis. Retrieved from http://www.cdc.gov
Centers for Disease Control and Prevention (CDC). (2014f). Pertussis (whooping cough): clinical complications. Retrieved from http://www.cdc.gov
Centers for Disease Control and Prevention (CDC, 2013a). Pertussis (whooping cough): clinical features. Retrieved from http://www.cdc.gov
Centers for Disease Control and Prevention (CDC, 2013b). Pertussis (whooping cough): vaccines and immunizations. Retrieved from http://www.cdc.gov
Centers for Disease Control and Prevention (CDC). (2013c). Pertussis (whooping cough): diagnosis confirmation. Retrieved from http://www.cdc.gov
Centers for Disease Control and Prevention (CDC). (2013d). Pertussis (whooping cough): specimen collection: proper technique for obtaining a nasopharyngeal specimen for isolation of Bordetella pertussis. Retrieved from http://www.cdc.gov
Centers for Disease Control and Prevention (CDC) (2013e). Pertussis (whooping cough): best practices for healthcare professionals on the use of polymerase chain reaction (PCR) for diagnosing pertussis. Retrieved from http://www.cdc.gov
Centers for Disease Control and Prevention (CDC). (2013f). Pertussis (whooping cough): treatment: timing and antimicrobial choice. Retrieved from http://www.cdc.gov
Centers for Disease Control and Prevention (CDC). (2013g). Pertussis (whooping cough): pertussis diagnosis and treatment. Retrieved from http://www.cdc.gov
Centers for Disease Control and Prevention (CDC) (2012). Updated recommendation for use of tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine in adults 65 years and older: Advisory Committee on Immunization Practices (ACIP). MMWR, 61(25), 468–70. Retrieved from http://www.cdc.gov
Centers for Disease Control and Prevention (CDC). (2009). Guideline for disinfection and sterilization in healthcare facilities, 2008. Retrieved from http://www.cdc.gov
County of Los Angeles, Department of Public Health (LADPH). (2014). Acute communicable disease control manual. Pertussis (whooping cough). Retrieved from http://www.publichealth.lacounty.gov
Cronan KM. (2011). KidsHealth from Nemours: pyloric stenosis. Retrieved from http://kidshealth.org
Leoffelholz M. (2012). Towards improved accuracy of Bordetella pertussis nucleic acid amplification tests. J Clin Microbio. Doi:10.1128/JCM.00612-12. Retrieved from http://jcm.asm.org
National Health Service (NHS). (2013). Whooping cough: complications. Retrieved from http://www.nhs.uk
Parch L. (2014). Why whooping cough is rising despite a new vaccine. Retrieved from http://www.webmd.com
Public Health Agency of Canada (PHA). (2010). Bordetella pertussis: pathogen safety data sheets: infectious substances. Retrieved from http://www.phac-aspc.gc.ca
Roush S. (2014). Enhancing surveillance: manual for the surveillance of vaccine-preventable diseases. Retrieved from http://www.cdc.gov
Todar K. (2012). Bordetella pertussis and whooping cough. Online textbook of bacteriology. Retrieved from http://textbookofbacteriology.net
U.S. Food and Drug Administration (USFDA). (2013). News release: FDA study helps provide an understanding of rising rates of whooping cough and response to vaccination. Retrieved from http://www.fda.gov