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The World Health Organization estimated
in 2002 that nearly 300,000 children died from pertussis.1 In
the United States, in spite of widespread vaccination there has
been a steady rise in the number of pertussis cases reported to
the Centers for Disease Control and Prevention (CDC) over the past
the last decade, punctuated by several statewide outbreaks in 2004
and 2005.2-5
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Pertussis occurs year-round in the United States, although the
disease peaks in the summer and fall in most locations. Humans are
the only reservoir for Bordetella pertussis, and
transmission from person to person occurs via respiratory droplets.
Attack rates following household exposure have been reported as
high as 90% for unimmunized children.6-8 Attack
rates in adult household contacts are at least 30%.6 Communicability
is highest early in the disease, but may persist for weeks in some
individuals.8 Unrecognized disease serves as a
reservoir for spread of infection.
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Infants younger than 6 months of age have the highest burden
of disease.9 Hospitalizations and mortality from
pertussis are highest in infants under 3 months of age.10 Passively
acquired transplacental antibodies afford little protection, and
vaccine-induced immunity requires multiple immunizations. Based
on CDC surveillance data from 2000 to 2003, 86% of hospitalizations
for pertussis occur in infants less than 3 months of age.10 Apnea
and respiratory distress were the most frequent complications, followed
by pneumonias. Mortality is greatest in infants less than 3 months
of age. The frequency of complications decline with increasing age;
however, protracted cough (> 3 months), sleep disturbances, and weight
loss are common in adults with pertussis; subcutaneous emphysema,
pulled muscles, and even broken ribs may occur in adults following paroxysmal
coughing.11,12
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In 2006 in the United States, infants younger than 6 months old
had the highest reported rate of pertussis (84.21 per 100,000 population),
but adolescents aged 10 to 19 years and adults older than 20 years
contributed the greatest number of reported cases.4 The
characteristic “whoop” is often absent in older
individuals. It is not until the nagging, forceful cough has persisted
for 2 or more weeks that adolescents and adults come to medical
attention. Even then, diagnosis may be delayed or disease may go
unrecognized because of a low index of suspicion.13 Adult caretakers
with undiagnosed pertussis are frequently found to be the source
for pertussis in infants.14 Nosocomial spread by
health care workers has been well documented.15,16
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Bordetella are small, fastidious, aerobic gram-negative
coccobacilli that require enriched media for isolation. B
pertussis is a respiratory pathogen of humans only and
is the sole cause of epidemic pertussis. B parapertussis is
a closely related species that accounts for less than 5% of
clinical pertussis.17B bronchiseptica occasionally causes
disease in the immunocompromised host but is better recognized as
a veterinary pathogen.18 Only B pertussis elaborates
pertussis toxin....