Pertussis (whooping cough) is an
acute respiratory disease caused by the bacterium Bordetella pertussis1. It causes violent coughing spells,
which makes a person difficult to breathe. It becomes paroxysmal between 1-2
weeks and often followed by a characteristic whooping noise. B. pertussis is an aerobic,
gram-negative aerobic coccobacillus1. It transmits from person to
person via airborne droplets containing the bacteria during sneezing or
produces a number of virulence factors that interact with host cells and alter their
functions. Filamentous hemagglutinin, pertactin and agglutinogen serve as adhesion
molecules help to anchor B. pertussis to
the ciliated respiratory epithelial cells3. While tracheal cytotoxin
releases nitric oxide which paralyze the cilia, stopping them from beating. This
hinders the ability to mechanically remove mucus and debris. Mucus starts
building up which triggers a violent cough reflex to clear the airway. Besides,
pertussis toxin (PT) is a protein exotoxin secreted exclusively by B. pertussis. PT also helps with the
binding of host target cells. In addition, it induces lymphocytosis and
increases histamine sensitivity, which makes it easier for fluid to seep out of
the blood vessels and into the airways tissues. This makes the airways swell
up, making it harder to breathe, and causes the classic “whopping” sound during
a coughing fit. Next, adenylate cyclase toxin catalyzes excessive CAMP
production, compromising phagocytosis4.
The incubation period of pertussis
usually lasts about a week. Early symptoms at catarrhal phase include sneezing,
runny nose, low-grade fever and a mild, occasional cough. Pertussis is highly
contagious at this phase and usually lasts about 2 weeks. The cough gradually
becomes more severe. The paroxysmal phase begins which lasts another 1-6 weeks
or more. It presents with uninterrupted fits of coughing followed by a whooping
sound. This violent coughing force can cause vomiting and exhaustion. While,
young infants often present with symptoms of apnea and cyanosis without cough.
At convalescent phase, which lasts between 2-3 weeks, the frequency and
intensity of cough decreases gradually5, 6.
The gold standard to diagnose
pertussis is bacterial culture due to its high specificity6.
Nasopharyngeal (NP) swab specimens should be obtained during the first 2 weeks
of illness when the viable bacteria are still present. Sensitivity reduces and
risk of false negative results increases at the later course of illness7.
Bacteria DNA can also be detected by polymerase chain reaction (PCR). PCR has
fast turnaround time and high sensitivity. However, PCR tests vary in
specificity. Thus, culture confirmation of pertussis should be obtained for
diagnosis. PCR should be tested from NP specimens taken at 0-3 weeks following
cough onset, but it may give accurate results for up to 4 weeks6, 7.
Serologic testing is useful for diagnosis in the later stage of disease. It can
be performed from 2-12 weeks following cough onset. Antibody levels are at
their highest between 2-8 weeks following cough onset, which is the ideal time
for specimen collection6, 7.
According to World Health
Organization (WHO), the incidence of pertussis increasing despite childhood
vaccination programmes. Pertussis outbreaks involving adolescents and young
adults have been reported8. This is probably due to the transition
to a newer vaccines6. Whole-cell (wP) vaccines based on dead B. pertussis bacteria, were initially
introduced in the industry. Lately in the 80s, many developed countries have
replaced wP with acellular (aP) vaccines as means of decreasing the
reactogenicity of the vaccine9. The aP vaccines based on highly
purified pertussis antigens. It was found that aP vaccines work well but has a shorter
duration of protection than the wP vaccines. The aP vaccines immunity wanes
rapidly over time. This leads to a limited impact of aP vaccines on infection
and transmission of pertussis to others. Besides, the resurgence of pertussis
may be due to increased recognition and diagnosis of pertussis as well as reduced
boosting immunity by circulating B. pertussis9.
Pertussis continues to be an
international public health concern as it has been a major cause of childhood morbidity
and mortality nowadays. Babies who get pertussis are usually infected by their
parents, siblings or caregivers who might not even know they have the disease10.
Pertussis is highly contagious and dangerous in infants especially those under
6 months of age. Babies infected with pertussis will require treatment in the
hospital. The most common and sometimes deadly complications are pneumonia and
apnea. It can also causes seizures and encephalopathy due to decrease oxygen levels
in the brain. Other complications include weight loss, ear infection and
dehydration. Adolescents and adults may also develop less serious complications
such as rib fracture difficulty sleeping, and urinary incontinence6,
Vaccination plays an important role
in preventing and reducing the risk of severe pertussis in infants and young
children. There are vaccines for babies, children, teens and adults. DTaP is
the childhood vaccine, which consists of 5 doses, typically given at age of 2
months, 4 months, 6 months, 15-18 months and 4-6 years. Tdap is the pertussis
booster vaccine for teens and adults. Booster shot every 10 years is
recommended to maintain the protection10, 12.
Some strategies are implemented to
increase immunity within the populations and prevent early infant mortality. All
children worldwide must be vaccinated including HIV-positive individuals. Pregnant
women are advised to receive a dose of Tdap in the 2nd or 3rd
trimester and at least 15 days before the end of pregnancy. This may help to
develop antibodies and protect the newborns until they can get their own DTaP
vaccine at 2 months old. Vaccination of healthcare personnel especially who have
close contact with pregnant mothers and infants should also be prioritized to prevent
Last but not least, the main
treatment for pertussis is macrolide antibiotics, such as erythromycin and
azithromycin which can be used at the catarrhal phase of disease. Trimethoprim
sulfamethoxazole can also be used6, 9.