By Cathy Barenski, RN, BSN

The Organism

• Bordetella pertussis, a small, aerobic gram-negative coccobacillus.
• Bacteria can be isolated from respiratory secretions or (less often) by large aerosol droplets from the respiratory tract of infected persons (at a range of 5 feet or less).
• Bordetella parapertussis,a closely related organism causes a pertussis-like syndrome in humans.

Epidemiology

Distribution: Worldwide, with an estimated 40,000,000 cases & 360,000 deaths in 1994 (6).

Prevalence: Adult pertussis is under-reported, with many adult cases going unrecognized and frequently diagnosed as upper respiratory tract infections (URIs), bronchitis, and allergies. In the US, most reported cases are in children under age 5, with half of those occurring in infants under 1 year old. About 5,000 cases are reported in the US each year (5). In the US from 1982 to the present, there has been a modest upward trend in the pertussis attack rate. A major contributor to this increase in the rise in case-finding in adults (3).

Acquisition: Immunity from childhood vaccination wanes 5 to 10 years after the last dose (usually given at 4 to 6 years of age), with efficacy of the vaccine falling from 100% in the first year following vaccination to 46% in the seventh year (2).

Pertussis in the Normal Host

• Because no booster for pertussis is given beyond the age of 6 years in the US and elsewhere, virtually all adolescents and adults are susceptible (2).
• Many cases go unrecognized and diagnosed as URIs, bronchitis, and allergies, with an estimated 40% subclinical cases.

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Pertussis in Infants and Children

• Infants who are not yet fully immunized are at greatest risk for morbidity and mortality and have the highest annual incidence of disease (5).
• Fully immunized children (DTP vaccine administration should be given at 2, 4, and 6 months) are well protected until the age of 6 (2).

Pertussis in the Immunocompromised Host

• Bordetella bronchiseptica, traditionally produces respiratory tract illness in animals, however, several recent case reports in HIV infected patients have been made (4).

Diagnosis

Laboratory Diagnosis

• Culture of nasopharyngeal mucus is the "gold standard" for laboratory diagnosis. Dacron swab is recommended (results ­ when test material can be inoculated directly onto culture medium).
• Direct Fluorescent Antibody (DFA) staining of nasopharyngeal secretions can provide rapid presumptive diagnosis but requires an experienced lab technician; false positive and false negative results can occur.
• Polymerase Chain Reaction (PCR) and serologic test for diagnosis have not been standardized. These methods are best used as presumptive assays in conjunction with culture.

Clinical Diagnosis

Classic symptoms of pertussis include the characteristic whooping cough, vomiting, apnea, and cyanosis immediately after a paroxysm of coughing. The paroxysmal stage lasts 2 to 6 weeks and is followed by a convalescent stage during which nonparoxysmal cough may persist for many weeks, particularly during subsequent viral upper respiratory tract infections.

• The incubation period of pertussis in non-immunocompromised patients is 5 to 14 days. Disease may occur up to 21 days after exposure.
• Onset is insidious with symptoms of an URI such as a runny nose lasting for about a week (catarrhal stage).
• Fever is usually minimal, lasting 1-2 weeks.
• Cough begins during the catarrhal stage and progresses steadily, becoming paroxysmal (numerous, rapid coughing).
• Patient may appear well between bouts of coughing, and if no paroxysm of coughing occurs during the physical examination, the diagnosis may be missed (paroxysmal stage).
• Symptoms of pertussis are milder in previously vaccinated persons, and the diagnosis may be missed in adolescents and adults, who often have less characteristic symptoms.
• Infants less than six months of age present more commonly with coughing, vomiting, apnea, cyanosis, and bradycardia than with a "whooping" cough (2).

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Transmission

• Pertussis is highly contagious; secondary attack rates may exceed 80% among susceptible household contacts.
• Transmission occurs by direct contact with respiratory secretions or large aerosol droplets from the respiratory tract of infected persons, although it is rarely airborne.
• The period of communicability starts with the onset of the catarrhal stage and extends into the paroxysmal stage.
• In adults, 20-47% of those exposed to the disease develop infection.
• Lack of awareness of adult pertussis in patients with prolonged cough and the high incidence of subclinical disease (40%) results in intra-familial and nosocomial disease (5).

• Transmission of pertussis in hospital settings has been documented in numerous reports. The number of patients and staff who have developed clinical pertussis indicates that these outbreaks have been of limited size, and no deaths due to nosocomial transmission have been reported; however, their impact has been large. SeeTable 1.
• These outbreaks have resulted from failure to recognize and isolate infected infants and children, failure to recognize and treat disease in staff members, and failure to institute control measures rapidly.
• Either a health-care worker or a patient may introduce B. pertussis into the hospital or clinic, and subsequent transmission to patients or health-care workers (or both) may occur.
• The risk of developing pertussis for patients or staff during these outbreaks is often difficult to quantify because the "definition" of an exposure is not well defined. See Exposure Algorithm.

Prevention

• Immunization (2,7)

The Centers for Disease Control and Prevention (CDC) and infectious disease experts recommend the following guidelines for managing pertussis exposures:

• Isolate suspected or known infected patients using droplet precautions.
• Cohort exposed patients.
• Provide postexposure prophylaxis for all asymptomatic exposed employees patients and visitors.
• Evaluate all symptomatic employees for pertussis, and provide appropriate therapy.
• Furlough symptomatic employees during the first 5 days of their therapy.

Treatment

• Erythromycin is considered the drug of choice for treatment and prophylaxis of pertussis (children: 40 to 50 mg/kg per day in four divided doses; adults: 1 to 2 g/day).
• Among the three oral erythromycin formulations (estolate, ethyl-succinate and stearate), erythromycin estolate achieves highest concentrations in serum and respiratory secretions.
• Trimethoprim-sulfamethoxazole (children: trimethoprim 8 mg/kg per day, sulfamethoxazole 40 mg/kg per day in two divided doses; adults: trimethoprim 320 mg/day, sulfamethoxazole 1600 mg/kg per day) is an alternative for patients who do not tolerate erythromycin.
• Several small clinical trials show that newer macrolides, clarithromycin and azithromycin, are also effective to treat pertussis. Because erythromycin causes significant gastrointestinal side effects, many experts favor these newer macrolides. The recommended duration of therapy is 14 days.
• Pertussis symptoms may be ameliorated when effective antimicrobial therapy is started during either the catarrhal stage or within 2 weeks of cough onset. However, once the paroxysmal stage has begun, antimicrobial therapy has little effect on the course of illness and is indicated primarily to limit the spread of the organism to others. Patients are no longer infectious after 5 days of therapy.

*There is sufficient evidence to propose that widespread vaccination of children, teenagers, and adults with acellular vaccines will virtually eliminate pertussis, as was done with diphtheria (about 50% of an entire population had to be vaccinated before this was achieved for toxin-positive C. diphtheriae. Worldwide vaccination with acellular vaccines has the potential for eradicating B.pertussis (1,2,7,8).

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Table 1

Outbreaks of Pertussis in hospital settings indicating number of patients and staff with clinical disease and impact of outbreak (Adapted from APIC Meeting)

Author	Setting	Clinical Pertussis			Interventions	Cost
		# of patients	# of staff	# of staff
Kurt et al (1972)[30]	Pediatric Service	3	5	78 Staff	Closed ward to elective admissions; serologic studies on 341 staff	not noted
Linnemann et al. (1975)[31]	Pediatric hospital	17	13	487 Staff	Serologic studies on 487 staff; 436 staff vaccinated	not noted
Valenti et al, (1980)[43]	Pediatric hospital	2	5			no tnoted
Christie et al.(1994)[29]	Pediatric hospital		13	195 staff	78 excluded from work; erythromycin for 583 employees;	$85,400
Dougherty (personal communication Nov. 1993)	Community hospital	3	6	744 Staff	Erythromycin for 460 people; 99 excluded from work;	$16,459
Shefer et al. (1995)[44]	800-bed hospital	9	10		Erythromycin for 350 patients and 40 staff; 630 staff vaccinated	not noted
Wiblin, et al (in press 1997)[24]	640-bed hospital	3	13		298 employees & 60 patients had face-to-face exposure. Erythromycin for all high risk persons	$4357 for prophylaxis alone

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