Since 1984, there has been a slow and steady increase in the reported pertussis cases in the United States with ∼50% of the cases in persons >10 years old.1,2 The increase in reported pertussis cases over the last couple decades is postulated to be because of a greater awareness that pertussis is a major cause of prolonged cough in adolescents and adults as well as possibly the use of several less efficacious vaccines that have led to waning vaccine-induced immunity.1 Household contact with parents and older siblings is often the source of pertussis infection in infants who are unvaccinated or not fully immunized.3
The incidence of reported pertussis cases among US infants increased 49% (34.2–51.1 cases per 100,000 infants) in the 1990s compared with the 1980s.4 Also, a 44% increase in the infant mortality rate in the United States from pertussis (1.67–2.40 deaths per million infants) was observed in these same time periods.5 Additionally, the pertussis hospitalization rate among children <2 years of age in the United States increased 23% from 1994–1998 to 1999–2003 (35.0–42.9 hospitalizations per 100,000 children <2 years of age).6 Among all age groups, infants have the highest incidence of pertussis and account for the majority of hospitalizations and deaths.7
The primary objective of our study was to assess the correlation between the reported national increase in the incidence of pertussis cases among adults, adolescents, and children and the number of infants and young children admitted to our hospital with confirmed Bordetella pertussis infection. The secondary study objective was to assess the epidemiologic features, clinical findings, and hospital course of these patients.
Driscoll Children's Hospital (DCH) is a 200-bed quaternary care pediatric teaching hospital in Corpus Christi, Texas, which provides care to children from South Texas, most of whom are indigent and Hispanic.
Subjects were identified via a search of the laboratory information system at DCH for positive B. pertussis tests, including direct fluorescent antibody (DFA) and culture (1996–2002), and polymerase chain reaction (PCR; 2003–2006). Testing was performed by the reference laboratory of the Texas Department of State Health Services. All children admitted to DCH between January 1, 1996 and December 31, 2006 with a confirmed diagnosis of pertussis were included in the study; outpatients seen in the emergency department or clinic but not admitted were excluded. The number of pertussis admissions per 10,000 hospitalizations from all causes was calculated each year.
The medical records of subjects were retrospectively reviewed. Data were collected on age, gender, immunization status, disease symptoms, presence of sick contacts with a coughing illness, laboratory test results, previous antibiotic treatment, date of admission, length of hospital stay, requirement for oxygen therapy, pediatric intensive care unit (PICU) admission, requirement for mechanical ventilation or extracorporeal membrane oxygenation (ECMO), and mortality rate.
Descriptive statistics were performed with Sigmastat statistical software (SPSS Inc., Chicago, IL). The institutional review board at DCH approved this research project. Patient and parental informed consent was not required.
A total of 56 children (28 males) were hospitalized with a confirmed diagnosis of pertussis; 16 outpatients with pertussis were excluded. In the 56 hospitalized children, the diagnosis was confirmed by PCR in 40 patients, DFA 7, DFA and culture 7, PCR and culture 1, and culture only 1. The median age was 61 days (range: 21 days–10 years), and 44 children (78%) were younger than 4 months of age. The distribution by age was as follows: 0 to 1 month (12%); 1 to 2 months (36%), 2 to 4 months (30%); 4 to 6 months (11%); 6 to 12 months (4%); and 12 months or older (7%). Pertussis admissions ranged from 0 to 7.4 per 10,000 hospitalizations from 1996 to 2003, and from 16.3 to 27.4 per 10,000 hospitalizations from 2004 to 2006 (Fig. 1). Most admissions occurred in the months of May (20%) and July (20%) followed by June (14%) and April (11%).
Cough was present in all the patients. Other symptoms reported were cyanosis (66%), vomiting (48%), decreased oral intake (46%), respiratory distress (43%), apnea (43%), and fever (20%). Most cases (52%) had a sick contact identified. For those cases with one or more sick contacts, it was usually the mother (48%) followed by siblings (45%), grandparents (10%), the father (7%), and cousins (7%). Although 79% of patients were appropriately vaccinated for age (ie, they received all vaccines as scheduled for their age), only 11 (20%) had received 3 doses of a pertussis-containing vaccine, 17 (30%) patients had 2 doses, 26 (46%) 1 dose, and 2 (4%) patients had no doses. Most patients (73%) did not receive antibiotics before admission, and only 20% of patients were prescribed effective therapy (macrolides).
A total of 50% of patients had a leukocytosis, and the mean white blood cell (WBC) count was 23,700 (range: 7500–104,200); 88% of patients had a lymphocytosis, and 10% had increased immature neutrophils. Patients admitted to the PICU tended to have a higher WBC count (29,600 ± 26,000 cells/mm3) than those who were not (21,500 ± 9400 cells/mm3), but this difference did not reach statistical significance. The 2 highest WBC counts (104,200 and 73,200 cells/mm3) occurred in children who died. Blood, urine, and cerebrospinal fluid cultures were performed at admission on 30, 19, and 12 patients, respectively. All blood and cerebrospinal fluid cultures were negative. One patient had a positive urine culture with Enterobacter cloacae.
The mean hospital length of stay was 8.9 ± 8.4 days (range: 1–43 days). Oxygen therapy was required for 45% of patients. The mean length of oxygen therapy was 9.4 ± 8.6 days (range: 1–30 days). A total of 16 patients (29%) required PICU admission. The mean length of stay in the PICU was 10.2 ± 9.6 days (range: 1–29 days). Of these patients, 50% needed mechanical ventilation, and the mean length of mechanical ventilation was 11.6 ± 9.9 days (range: 2–29 days). Three (5%) patients died, and all the deaths occurred during the last 2 years of the study. All 3 patients who died were neonates (<30 days of age) and Hispanic. One patient had a polymicrobial catheter-related bloodstream infection, but all died of pneumonia and respiratory failure. Two of them received ECMO, and the third patient also required ECMO, but she died before it could be started.
We documented a rise in the number of pertussis admissions per 10,000 hospitalizations from all causes during the 11-year study period. Pertussis admissions ranged from 0 to 7.4 per 10,000 hospitalizations from 1996 to 2003, and from 16.3 to 27.4 per 10,000 hospitalizations from 2004 to 2006. The overall number of hospitalizations was steady from 1996 to 2006 (range: 6143–6961). Most patients (78%) were infants younger than 4 months of age who were unvaccinated or not fully protected as they had not yet received 3 doses of a pertussis-containing vaccine. This increase in pediatric pertussis hospitalizations in South Texas is consistent with the national trend of more pertussis admissions in children <2 years of age, and the rise of pertussis cases in adults and adolescents, who are often the source of infections in infants. We also observed 3 deaths from pertussis in Hispanic neonates. This matches other studies that found fatal cases usually occur in infants, particularly those who are <4 months of age.5,8,9 Additionally, the fatality rate has been reported to be 2.6 times higher among Hispanic infants than non-Hispanic infants (4.77 compared with 1.80 deaths per million infants),5,8 and our hospital serves predominately a Hispanic population.
Our results also were similar to those of several pertussis studies conducted in other countries. Elliott et al10 in a national study of infants hospitalized with pertussis in Australia in 2001 found that the most common source of infection was a sick parent followed by a sibling, just as we observed. Horcajada Herrera et al11 in a study from a children's hospital in Gran Canaria Island, Spain, from 2003 to 2007, also found household contacts to be the source of infection in at least 65% of infant pertussis cases. They also reported that complications occurred in 23% of hospitalized patients, and 6% died. About 29% of our patients required admission to the PICU of whom half needed mechanical ventilation, and 5% of our hospitalized patients died. Moraga et al12 in study of 11 hospitals from Catalonia, Spain, from 1997 to 2001, found that 82% of hospitalized infants were <4 months of age, and the deaths (0.8%) occurred in infants <2 months of age, which was similar to our results. They also recorded comparable rates of symptoms in their patients (cough 95%, cyanosis 68%, vomiting 37%, apnea 28%). Mikelova et al13 in a study of 16 pertussis deaths in Canada, from 1991 to 2001, identified leukocytosis as an independent predictor of a fatal outcome. Two of our 3 neonates who died had very high white blood cell counts (>70,000 cells/m3) that were 3- to 4-fold greater than the mean.
Pertussis is still an important cause of hospitalization in children, especially young infants who are not fully immunized against it. To provide protection to these infants, physicians, and public health authorities should implement the Advisory Committee on Immunization Practices recommendations for the vaccination of adolescents, adults, and postpartum women.14–16 Our findings highlight the importance of pertussis vaccination for women in the immediate postpartum period as well as vaccination of all household members who are the likely source of infection according to the recommendations of Advisory Committee on Immunization Practices.
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