pertussis is an acute respiratory tract infection caused by bordetella pertussis ; this infection is most severe in infants .
there are still 60 million cases of pertussis each year worldwide , resulting in about 300,000 deaths1 ) .
however , pertussis cases are increasing in western countries with high vaccination coverage since the 1990s2 ) .
in korea , an average of approximately 11.5 cases of pertussis is reported to the korea center for disease control and prevention ( kcdc ) each year , and there have been no fatalities since the 1990s3 ) . however , in the 2000s , the pertussis cases reported tended to increase , with up to 66 cases being reported in 20094 , 5 ) . since the diagnosis of the reported cases was confirmed by pcr and culture without serology ,
this article was intended to review the latest knowledge about the pathogenesis , epidemiology , diagnosis , treatment , and prevention of pertussis .
pertussis is a mucosal infection whose pathogenesis is induced by the local and systemic effects of toxins .
more than 95% of pertussis cases occur during epidemics and in endemic areas and are caused by b. pertussis infection ; the remaining 5% of cases are caused by infection with bordetella parapertussis6 ) .
possess the pertussis toxin ( pt ) , which is the bacteria 's major virulence protein that infects only humans .
b. pertussis organisms are acquired through aerosols and have strict tropism for the ciliated epithelium of the respiratory tract . attachment to target cells
is mediated by filamentous hemagglutinin ( fha ) , some agglutinogens ( especially fim2 and fim3 ) , a 69-kd nonfimbrial surface protein called pertactin ( prn ) , and pt .
bacterial survival is aided by ciliostasis related to the tracheal cytotoxin ( tct ) and impaired leukocyte function due to pt and the adenylate cyclase ( ac ) toxin . local epithelial damage and respiratory tract symptomatology
pt plays a major role in the severity of pertussis cough , encephalopathy , and lymphocytosis by preventing migration of the organism from the circulating blood7 ) .
pertussis is highly contagious , with attack rates as high as 100% in susceptible individuals who have been exposed to contaminated aerosol droplets at close range .
however , neither the disease nor vaccination confer complete or lifelong immunity against the disease or protect against reinfection .
protection against the typical disease begins to wane 3 to 5 years after vaccination and is not measurable by 12 years .
when exposed to pertussis infection , over 50% of vaccinated people develop asymptomatic , mild desease8 ) and become a source of infection for infants in whom pertussis may result in hospitalization and death .
pertussis is a significant cause of mortality in early infancy worldwide , despite widespread vaccination .
it remains endemic in many industrialized countries , which have reported increases in incidence during the past several decades .
this increase has been mainly among adults and adolescents , and chronic cough that persisted for over 2 weeks was the main cause ( 20 - 37.2% ) , although death and hospitalization from pertussis continue to occur predominantly in unvaccinated infants aged less than 6 months9 , 10 ) .
in korea , the incidence of pertussis has dramatically decreased since dtwp vaccination started in 1958 and dtwp was changed to dtap in 1982 .
the number of pertussis cases reported to the kcdc was approximately 11.5 cases each year until 1991 , but the incidence of pertussis seems to be on the rise since 2000 , although the vaccination rate continues to be over 94% . in 2009 , 66 cases of pertussis were reported .
the kcdc confirmed that these cases were pertussis by culture or pcr of pertussis from nasal specimens and a positive rate of culture and pcr is very low compared to serologic study . on the basis of the sensitivity of the test and reporting rate in 2009 , it can be assumed that more than 2,000 pertussis occurred in 2009 ( fig .
classical pertussis has 3 stages of clinical symptoms : catarrhal , paroxysmal , and convalescent .
nonspecific symptoms such as rhinorrhea , sneezing , mild fever , and eye infection without significant conjunctivitis occur after about 2 weeks in the catarrhal stage , and these symptoms are followed by characteristic paroxysmal stage symptoms such as a dry , intermittent , irritative hack which evolves into paroxysms . in the paroxysmal stage , a healthy - looking , playful toddler suddenly begins to express an anxious aura and experiences bouts of uninterrupted coughing while drawing a single breath .
the coughs are followed by a loud whoop as inspired air passes through the still partially closed glottis ( fig .
3 months , the catarrhal phase usually lasts for a few days or is not recognized at all ; the paroxysmal and convalescent stages are protracted , with periods of spasmodic coughing throughout the first year of life . in the paroxysmal stage , young infants frequently present with gagging , gasping , choking , cyanosis , apnea , or an " apparent life - threatening event " instead of paroxysmal coughing ; whooping is absent .
in immunized children and adults , all stages of pertussis are shortened , and it is not uncommon for the disease to not have distinct stages and show chronic cough paroxysms that continue for more than 2 weeks .
the principal complications of pertussis are apnea ; secondary infections such as pneumonia and otitis media ; respiratory failure because of apnea , pneumonia , or pulmonary hypertension ; and physical sequelae because of forceful coughing .
pertussis - related complications and mortality are reported , especially in patients younger than 2 months , who have the highest reported rates of pertussis - associated hospitalization ( > 90% ) , pneumonia ( 15 - 25% ) , seizures ( 2 - 4% ) , encephalopathy ( 0.5 - 1% ) , and death ( 0.5 - 1%)11 - 13 ) .
there are several reports on pertussis as a significant cause of sudden infant death syndrom14 - 16 ) .
pertussis should be considered as a diagnosis in very young infants who have not completed 3 doses of vaccination and have classical symptoms or in children who display major symptoms such as chronic paroxysmal cough without significant fever , general weakness , and sore throat and do not have physical signs such as wheezing and rales .
chlamydia trachomatis infection in very young infants and adenovirus , mycoplasma pneumoniae , and chlamydia pneumoniae infections should be the differential diagnosis for children because despite the abovementioned differences , it is not easy to diagnose pertussis on the basis of only clinical symptoms and signs , especially if secondary infections such as pneumonia are present . the laboratory finding characteristic for pertussis is leukocytosis ( leukocyte counts of 15,000 - 100,000 cells / mm due to absolute lymphocytosis in the late catarrhal and paroxysmal stages .
the degree of leukocytosis parallels the severity of illness and is mainly observed in unvaccinated children ; leukocytosis is not common in adolescents , adults , and partially immunized children with pertussis17 , 18 ) .
chest x - ray findings are normal in most cases , although chest x - ray images of hospitalized young infants may show hilar infiltration , interstitial edema , atelectasis , and , rarely , pneumothrax
. there are several ways to confirm b. pertussis infection such as serology , culture , direct fluorescent antibody ( dfa ) testing , and pcr .
the traditional gold standard for confirming pertussis is culture , but many factors that can influence the results , such as the stage of illness , use of antibiotics , cautious posterior nasopharyngeal sampling , adequate transport media ( regan - lowe ) and culture media ( regan - lowe charcoal media with 10% horse blood or 5 - 40 g / ml cephalexin ) , and vaccination status of the patient . in adolescents and adults with pertussis , culture or pcr test results
are positive in < 10% of cases that have been confirmed as pertussis by serology . however , pcr is more rapid and sensitive than culture for confirming pertussis19 ) .
serologic tests use enzyme immunoassay ( eia ) to detect antibodies to components of b. pertussis and are the most sensitive tests for diagnosis in distantly immunized individuals and those evaluated after the second week of experiencing coughs . a 4-fold increase in anti -
pt igg with 4 - 6 week intervals appears to be the most reliable serologic test , and a single test showing an anti - pt igg level of > 94 - 110 eu / ml ( over 2sd of the igg level in the community ) has been proposed as the diagnostic cutoff point20 ) .
the goals of therapy are to limit the number , severity , and duration of paroxysms and prevent complications .
hospitalization is usually needed to treat infants with pertussis because they need supportive care such as hydration , nutrition , and monitoring for complications .
if the patient experienced uncontrolled severe cough along with hypoxia , seizures , and apnea , ventilator care should be provided along with muscle paralysis to prevent bradycardia and cardiopulmonary complications .
antibiotics should be given to infants younger than 1 year old who have had the cough paroxysm for less than 6 weeks and to all the patients who began coughing within 3 weeks in order to improve symptoms , shorten their duration , and prevent further infection21 ) .
erythromycin is the treatment of choice ; 40 - 50 mg / kg erythromycin is prescribed for 10 - 14 days .
newer macrolides such as clarithromycin and azithromycin can be used instead of erythromycin and have the same effect22 ) .
since pertussis is extremely contagious , there have been many secondary cases and outbreaks of pertussis in hospitals and chronic - care facilities . to prevent infection from the index patient ,
droplet precautions are recommended for at least 5 days after the initiation of macrolide therapy and those who have had close exposure should get the same macrolide treatment as pertussis patients .
in addition , children younger than 7 years who did not complete the 5 rounds of pertussis vaccination should complete the schedule of vaccination .
adolescents older than 11 years and adults should receive the tdap ( tetanus toxoid , diphtheria toxoid , acellular pertussis ) : booster vaccination .
the current pertussis vaccination schedule in korea comprises a primary series of 3 vaccinations : the first dose is administered at 2 months of age , the second is a booster vaccination given at 18 months of age , and the third dose is also a booster vaccination given at 4 - 6 years of age . despite longstanding and widespread vaccination programs ,
pertussis remains endemic in many industrialized countries , including australia , canada , italy , japan , the netherlands , switzerland , and the united states , all of which have reported recent increases in incidence .
factors contributing to pertussis resurgence remain unclear , but possible causes are waning immunity , improved surveillance and diagnosis , and adaptation of circulating b. pertussis strains23 , 24 ) .
although pertussis is classically a disease of infants and children , the main portions of the population showing an increased incidence of pertussis are adults and adolescents ; these infected adolescents and adults become a source of infection for infants .
the problem of waning immunity after pertussis vaccination and disease , tdap booster vaccination for adolescents older than 11 years and adults has been started since 2006 in the united states and was introduced in korea in 2009 .
pertussis was a leading cause of death of children before pertussis vaccination was started , and the disease continues to be a leading cause of child mortality .
the incidence and mortality of pertussis has been increasing since 1990 in developed countries despite these countries having vaccination rates of 95% . after widespread vaccination , the diagnosis of pertussis is difficult because of lack of classical clinical manifestations in very young infants and vaccinated children . in korea ,
the prevalence of pertussis might be increasing since 2000 and there was a pertussis outbreak in 2009 .
no epidemiological study based on serology has been done so far in korea , and the exact number of pertussis cases that occur and are undiagnosed remains unknown .
therefore , we do not have any weapons to fight against future outbreaks of pertussis , a significant cause of mortality of very young infants .
therefore , i suggest that a nationwide epidemiologic study of pertussis be undertaken immediately . the study should aim to develop methods for serologic diagnosis , new devise vaccination strategies to prevent waning immunity and reduce the number of very young unvaccinated individuals , and develop diagnosis criteria for atypical pertussis .
 pertussis is a highly contagious respiratory tract disease caused by bordetella pertussis infection 
 . the clinical manifestation of this infection can be severe enough to cause death . 
 although pertussis has been supposed to be a vaccine - preventable disease ever since the widespread vaccination of children against pertussis was started , since the 1990s , cases of pertussis and related fatalities are on the rise , especially in countries with high vaccination coverage . in korea , there have been no deaths due to pertussis since 1990 , and the vaccination rate continues to be approximately 94% . 
 however , the number of pertussis cases reported to the korea center for disease control and prevention has tended to increase in the 2000s , and in 2009 , there was an obvious increase in the number of pertussis cases reported . 
 this review aims to present the latest information about the pathogenesis , diagnosis , treatment , and prevention of pertussis . 