Haemophilus influenzaeType b Invasive Disease and Meningitis
I. Disease Description
Haemophilus influenzae (Hi) invasive disease is caused by the bacterium Haemophilus influenzae. Hi may be either encapsulated (typeable) or unencapsulated (nontypeable). Six antigenically distinct capsular types of Hi (types a–f) that can cause invasive disease in persons of any age have been identified. Nontypeable strains may also cause invasive disease but are less virulent than encapsulated strains and cause only infrequently serious infection in children.
I. Disease Description
Haemophilus influenzae (Hi) invasive disease is caused by the bacterium Haemophilus influenzae. Hi may be either encapsulated (typeable) or unencapsulated (nontypeable). Six antigenically distinct capsular types of Hi (types a–f) that can cause invasive disease in persons of any age have been identified. Nontypeable strains may also cause invasive disease but are less virulent than encapsulated strains and cause only infrequently serious infection in children.
Meghan had Hib meningitis before the vaccine. She is deaf. Thre is a vaccine now. Hib is a required vaccine for infants.
Invasive H. influenzae diseases include clinical syndromes of meningitis, bacteremia or sepsis, epiglottitis, pneumonia, septic arthritis, osteomyelitis, pericarditis, and cellulitis. In contrast, syndromes of mucosal infections such as bronchitis, sinusitis, and otitis media are considered noninvasive disease. The noninvasive syndromes are not nationally notifiable.
Before the introduction of effective vaccines, H. influenzae serotype b (Hib) was the cause of more than 95% of invasive Hi diseases among children younger than 5 years of age. Hib was the leading cause of bacterial meningitis in the United States among children younger than 5 years of age and a major cause of other life-threatening invasive bacterial diseases in this age group. Meningitis occurred in approximately two-thirds of children with invasive Hib disease, resulting in hearing impairment or severe permanent neurologic sequelae, such as mental retardation, seizure disorder, cognitive and developmental delay, and paralysis in 15%–30% of survivors. Approximately 4% of all cases were fatal.1
Invasive H. influenzae diseases include clinical syndromes of meningitis, bacteremia or sepsis, epiglottitis, pneumonia, septic arthritis, osteomyelitis, pericarditis, and cellulitis. In contrast, syndromes of mucosal infections such as bronchitis, sinusitis, and otitis media are considered noninvasive disease. The noninvasive syndromes are not nationally notifiable.
Before the introduction of effective vaccines, H. influenzae serotype b (Hib) was the cause of more than 95% of invasive Hi diseases among children younger than 5 years of age. Hib was the leading cause of bacterial meningitis in the United States among children younger than 5 years of age and a major cause of other life-threatening invasive bacterial diseases in this age group. Meningitis occurred in approximately two-thirds of children with invasive Hib disease, resulting in hearing impairment or severe permanent neurologic sequelae, such as mental retardation, seizure disorder, cognitive and developmental delay, and paralysis in 15%–30% of survivors. Approximately 4% of all cases were fatal.1
II. Background
Before the introduction of Hib conjugate vaccines for infants in late 1990, an estimated 20,000 children younger than 5 years of age (approximately 1 in 200 children) developed invasive Hib disease each year in the United States; nearly two-thirds of all cases occurred among children younger than 18 months. By 2000, the incidence of all Hi invasive disease among children younger than 5 years of age reported to CDC declined by 96%—from 41 cases per 100,000 in 1987 to 1.6 cases per 100,000 in 2000.2–5 Laboratory-based surveillance data from the Active Bacterial Core surveillance (ABCs) system, which included serotype information on all invasive Hi isolates, provided direct evidence of a decline in Hib disease. From 1989 to 2000, there was a 99% reduction in Hib invasive disease among children younger than 5 years of age, which coincided with the introduction and use of Hib conjugate vaccines among infants and children.2–5 Continued monitoring of Hi invasive disease through ABCs demonstrated a decrease in invasive Hib rates in children younger than 5 years of age, with the average incidence from 2000 to 2004 being 0.14 cases per 100,000.6–10
Because Hib has become a rare cause of invasive disease in the United States, the need to correctly identify the serotype of Hi isolate from any invasive disease has increased. Serotyping by slide agglutination can sometimes be inaccurate, especially since it is not performed routinely in most laboratories. One study found that 28 (70%) of 40 Hi isolates from ABCs sites that had been reported as "Hib" to CDC were actually nontypeable Hi isolates.11 Another study found discrepancies between the results of slide agglutination subtyping performed at state health departments and those of polymerase chain reaction (PCR) capsule typing performed at CDC for 56 (40%) of 141 isolates.12 Accurate serotype data on all Hi isolates from children younger than 5 years of age is critical for monitoring Hib vaccine effectiveness. These studies emphasize the importance of quality control and quality assurance in laboratory serotyping.
III. Importance of Rapid Case Identification
Rapid case identification is important for early administration of Hib vaccine and, if needed, for chemoprophylaxis to household and childcare classroom contacts of case-patients.13 In addition, early notification of Hi invasive disease cases in children younger than 5 years is needed to obtain the Hi isolate before it is discarded so that it can be serotyped. State health departments with questions about serotyping should contact the CDC Meningitis and Vaccine-Preventable Diseases Branch laboratory at 404-639-3158.
IV. Disease Reduction Goals
Hib disease has declined rapidly because of widespread immunization of infants and young children with conjugate vaccines and because humans are the only known reservoir for Hib. The elimination of Hib disease among children younger than 5 years of age in the United States has been proposed as an objective for the year 2010.
Resouce www.CDC.gov
Because Hib has become a rare cause of invasive disease in the United States, the need to correctly identify the serotype of Hi isolate from any invasive disease has increased. Serotyping by slide agglutination can sometimes be inaccurate, especially since it is not performed routinely in most laboratories. One study found that 28 (70%) of 40 Hi isolates from ABCs sites that had been reported as "Hib" to CDC were actually nontypeable Hi isolates.11 Another study found discrepancies between the results of slide agglutination subtyping performed at state health departments and those of polymerase chain reaction (PCR) capsule typing performed at CDC for 56 (40%) of 141 isolates.12 Accurate serotype data on all Hi isolates from children younger than 5 years of age is critical for monitoring Hib vaccine effectiveness. These studies emphasize the importance of quality control and quality assurance in laboratory serotyping.
III. Importance of Rapid Case Identification
Rapid case identification is important for early administration of Hib vaccine and, if needed, for chemoprophylaxis to household and childcare classroom contacts of case-patients.13 In addition, early notification of Hi invasive disease cases in children younger than 5 years is needed to obtain the Hi isolate before it is discarded so that it can be serotyped. State health departments with questions about serotyping should contact the CDC Meningitis and Vaccine-Preventable Diseases Branch laboratory at 404-639-3158.
IV. Disease Reduction Goals
Hib disease has declined rapidly because of widespread immunization of infants and young children with conjugate vaccines and because humans are the only known reservoir for Hib. The elimination of Hib disease among children younger than 5 years of age in the United States has been proposed as an objective for the year 2010.
Resouce www.CDC.gov