puts patients at increased risk for secondary pneumonia. Also, this patient required intubation for respiratory support, which further increases the risk of health care-associated pneumonia due to organisms such as methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa.
5. Historically, vaccination against pertussis was recommended at ages 2 months, 4 months, 6 months, 15 to 18 months, and 4 to 6 years. This patient was too young to have received any pertussis vaccine. Based on laboratory testing, the mother was confirmed to have pertussis, but the brother could not be confirmed due to the extended time since his illness. Nonetheless, it is probable that the brother also had pertussis. The possibilities are that neither the mother nor the brother was vaccinated against pertussis in childhood, or the fact that the protection offered by the vaccine wanes within 5 to 10 years of administration. In fact, both the mother and brother had been vaccinated in childhood, so the latter possibility is a likely explanation. Another possibility is these two individuals, closely genetically related, could not mount an immune response to the pertussis vaccine antigens. Studies have shown that vaccine-induced immunity wanes after the fifth dose of pertussis vaccine. In this case, the older sibling likely got pertussis from his peers and then infected the mother, who was infectious at the time of the infant’s birth. The infant’s lack of protective immunity, along with the high infectivity of pertussis, made it very likely that the infant would get pertussis.
Vaccination against pertussis using a whole-cell vaccine began in the 1940s. This vaccine was combined with diphtheria (D) and tetanus (T) toxoids to make the combination DTP vaccine that was given to infants and toddlers. With widespread immunization, the incidence of pertussis decreased from 157 cases per 100,000 people to <1 per 100,000 in the 1970s. However, the whole-cell vaccine was associated with increased mild side effects such as erythema, swelling, and tenderness at the injection site; fever; drowsiness; and anorexia; as well as severe side effects such as high fever and seizures. Whole-cell vaccines were considered too reactogenic for use in adolescents or adults. Acellular pertussis vaccines, which have fewer side effects, were introduced in the 1990s to replace whole-cell vaccines. These vaccines target the primary virulence factors of B. pertussis and contain purified proteins including detoxified pertussis toxins and adhesins. The acellular vaccine is combined with DT for the DTaP vaccine given to children in a five-dose series that is completed by age 4 to 6. Neither natural pertussis infection nor vaccine-induced protection provides long-term immunity. Several studies have since shown that the acellular pertussis vaccine is not as effective as the whole-cell vaccine, making children 7 to 10 years old particularly vulnerable as a reservoir of pertussis transmission. In 2012, there were >41,000 cases of pertussis reported in the United States and likely many more that were not diagnosed and/or reported. In addition, the number of outbreaks due to pertussis has increased. A well-described outbreak in California occurred in 2010 in which 89% of cases were among infants <6 months old, with the next highest incidences in those 7 to 9 years old and 10 to 18 years old. In 2012, Washington state had >2,500 pertussis cases in 6 months, with the highest incidence in infants <1 year and children aged 10, 13, and 14 years. In 2012, 49 states reported increases in pertussis cases relative to the previous year. Better detection methods (e.g., PCR) are partially responsible for this increase, but so is natural pertussis epidemiology. It has been estimated that 13 to 20% of adolescents and adults with prolonged cough have pertussis. Diagnosing older individuals with pertussis is problematic because they often have an atypical presentation consisting of nothing more than a chronic cough. However, these individuals are common sources of infant infections, particularly parents, primary caregivers, siblings, and health care workers. Since infants are at the greatest risk for serious illness and death due to pertussis, these sources of transmission are primary targets for new vaccination strategies.
In 2005, two tetanus, diphtheria, and acellular pertussis vaccines, Tdap and DTaP, were approved for administration: DTaP for people 11 to 64 years old and Tdap for those 10 to 18 years old. Tdap vaccine has reduced antigen doses for diphtheria and pertussis compared to DTaP. The Advisory Committee on Immunization Practices now recommends Tdap vaccination for 11- to 12-year-olds, adults who have not previously received Tdap or with unknown vaccine status, and pregnant women during each pregnancy. In addition, many health care institutions are requiring Tdap vaccination of all health care personnel. It is hoped that these new vaccination strategies will break the chain of transmission of a pathogen that only infects humans.
6. Hospitalized patients with pertussis should be on droplet precautions as pertussis is transmitted by large respiratory droplets produced when coughing, sneezing, or talking. Pertussis is highly communicable, with household attack rates of 80 to 100%. Droplet precautions should be maintained until the patient has received 5 days of appropriate antimicrobial therapy. There is no evidence of fomite transmission, which would require contact precautions as well. Close contacts of a person diagnosed with pertussis should be assessed for the infectiousness of the patient (e.g., which stage of disease), the intensity of the exposure, and the risks to the contact of getting pertussis or transmitting it to vulnerable populations (e.g., infants, pregnant women, and health care personnel). If warranted, postexposure prophylaxis with a macrolide should be administered to contacts within 21 days of onset of cough in the index patient. Alternatively, low-risk contacts can be monitored for pertussis symptoms for 21 days.
REFERENCES
1. Guiso N. 2009. Bordetella pertussis and pertussis vaccines. Clin Infect Dis 49:1565–1569.
2. Klein NP, Bartlett J, Rowhani-Rahbar A, Fireman B, Baxter R. 2012. Waning protection after fifth dose of acellular pertussis vaccine in children. N Engl J Med 367:1012–1019.
3. Loeffelholz M. 2012. Towards improved accuracy of Bordetella pertussis nucleic acid amplification tests. J Clin Microbiol 50:2186–2190.
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CASE 10
In December 2009, a 45-year-old female presented to the emergency department (ED) 2 days following abrupt onset of sore throat, nonproductive cough, chills, and mild fever. A chest radiograph was performed, which was normal. She was diagnosed with bronchitis and asked to follow up with her primary care physician, who subsequently started her on levofloxacin and albuterol. Four days later she presented again to the ED with worsening cough, dyspnea, fever (38.3°C; 101°F), and generalized lethargy. Additionally, she reported new symptoms including a global headache, dizziness, myalgias, and arthralgias. She had no abdominal pain, but reported nausea and anorexia. Her chest radiograph showed diffuse reticulonodular opacities throughout the left lung, which were not present on her visit 4 days previously. The patient was admitted for further evaluation. Questioning revealed the following: she had a history of diabetes and hypertension, she smoked an average of a pack of cigarettes daily, and she had received the seasonal influenza vaccine. Her husband was recently
