Comparison of erythromycin estolate and erythromycin ethylsuccinate for treatment of pertussis. The Erythromycin Study Group

Effect of Macrolides and β-lactams on Clearance of Bordetella pertussis in the Nasopharynx in Children With Whooping Cough

OBJECTIVE

The purpose of the current study is to investigate the bactericidal effect of macrolides and β-lactams on Bordetella pertussis (B. pertussis) in the nasopharynx and provide guidance for treating macrolides-resistant B. pertussis infections.

METHODS

Patients with whooping cough was diagnosed by culture of nasopharynx swabs between January 2016 to December 2018. B. pertussis was identified using specific antisera against pertussis and parapertussis. Drug susceptibility test was carried out using the E-test method. The clearance of B. pertussis in nasopharynx at 7 and 14 days into and posttreatment with macrolides, and β-lactams was compared.

RESULTS

A total of 125 B. pertussis samples were collected from patients who received single antibiotic treatment. Among those isolates, 62.4% (78/125) had high resistance with minimum inhibitory concentrations greater than 256 mg/L for erythromycin and azithromycin. The MIC90 of piperacillin, cefoperazone-sulbactam, meropenem, ampicillin, ceftriaxone, ceftazidime and trimethoprim-sulfamethoxazole for these isolates was <0.016, 0.094, 0.094, 0.19, 0.19, 0.25 and 0.75 mg/L, respectively. The clearance rate with β-lactams treatment (68.8%, 44/64) was significantly higher than that with macrolides treatment at 14 days posttreatment (50.8%, 31/61) (χ2 = 4.18, P = 0.04). Macrolides had a better clearance rate at 7 days posttreatment than β-lactams (χ2 = 4.49, P = 0.03) for macrolides-sensitive isolates and a worse clearance rate for macrolides-resistant isolates.

CONCLUSION

B. pertussis isolates had a high-resistant rate for macrolides in our study. Macrolides are the first choice for treating pertussis caused by macrolides-sensitive strains, and some β-lactams such as piperacillin should be considered as alternative antibiotics for treatment of macrolides-resistant B. pertussis infection.

Pharmacotherapy for Bordetella pertussis infection. II. A synthesis of clinical sciences

Despite the plethora of studies that have examined laboratory susceptibility testing for Bordetella pertussis, assessments of treatment have lagged far behind both in quality and quantity. Macrolides and trimethoprim/sulfamethoxazole historically served the needs of both treatment and prevention, albeit there is still controversy about the degree of protection measured both bacteriologically and clinically. As high-level macrolide resistance has emerged in some geographic regions and since macrolides have been the mainstay of therapy, alternative antibiotics need to be defined for pertussis. In vitro susceptibility testing suggests the potential for several alternatives to macrolides, including trimethoprim/sulfamethoxazole, specific β-lactam agents, chloramphenicol, some quinolones and possibly some tetracyclines. For the latter antibiotics, more clinical studies for treatment and prophylaxis are required in to order to establish bacteriological-clinical correlates for outcome. In the interim, if the clinical circumstances mandate the use of proposed interim alternatives to macrolides, outcomes should be assessed with test of cure by culture, since genetic amplification technologies do not discriminate bacterial viability. Whereas there may be debate in regard to using placebo or macrolides as the controls for alternative antibiotic therapy in geographies where most B. pertussis isolates are antibiotic-susceptible, both placebo and macrolide controls should be assessed along with alternative antibiotics in well-designed controlled studies in regions pressured by macrolide resistance. Outcomes of clinical response and epidemiological patterns of disease should continue to be monitored given the degree of macrolide resistance that is emerging.

Finnish guidelines for the treatment of community-acquired pneumonia and pertussis in children

Evidence-based guidelines are needed to harmonise and improve the diagnostics and treatment of children's lower respiratory tract infections. Following a professional literature search, an interdisciplinary working group evaluated and graded the available evidence and constructed guidelines for the treatment of community-acquired pneumonia and pertussis.

CONCLUSION

The clinical guidelines state that chest radiography is not needed if the child is diagnosed with pneumonia and treated at home. Complications should be considered if there is no improvement after antimicrobial therapy and a paroxysmal cough can indicate pertussis, which is life-threatening in unvaccinated infants and can lead to respiratory failure.

Antibiotics for whooping cough (pertussis)

BACKGROUND

Whooping cough is a highly contagious disease. Infants are at highest risk of severe disease and death. Erythromycin for 14 days is currently recommended for treatment and contact prophylaxis, but is of uncertain benefit.

OBJECTIVES

To study the benefits and risks of antibiotic treatment of and contact prophylaxis against whooping cough.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), the Database of Abstracts of Reviews of Effects (DARE) (The Cochrane Library Issue 1, 2007); MEDLINE (January 1966 to March 2007); EMBASE (January 1974 to March 2007).

SELECTION CRITERIA

All randomised and quasi-randomised controlled trials of antibiotics for treatment of, and contact prophylaxis against, whooping cough.

DATA COLLECTION AND ANALYSIS

Three to four review authors independently extracted data and assessed the quality of each trial.

MAIN RESULTS

Thirteen trials with 2197 participants met the inclusion criteria: 11 trials investigated treatment regimens; 2 investigated prophylaxis regimens. The quality of the trials was variable.Short-term antibiotics (azithromycin for three to five days, or clarithromycin or erythromycin for seven days) were as effective as long-term (erythromycin for 10 to 14 days) in eradicating Bordetella pertussis (B. pertussis) from the nasopharynx (relative risk (RR) 1.02, 95% confidence interval (CI) 0.98 to 1.05), but had fewer side effects (RR 0.66, 95% CI 0.52 to 0.83). Trimethoprim/sulfamethoxazole for seven days was also effective. Nor were there differences in clinical outcomes or microbiological relapse between short and long-term antibiotics. Contact prophylaxis of contacts older than six months of age with antibiotics did not significantly improve clinical symptoms or the number of cases developing culture-positive B. pertussis.

AUTHORS' CONCLUSIONS

Although antibiotics were effective in eliminating B. pertussis, they did not alter the subsequent clinical course of the illness. There is insufficient evidence to determine the benefit of prophylactic treatment of pertussis contacts.

Pertussis immunisation in adolescents and adults –Bordetella pertussisepidemiology should guide vaccination recommendations

Pertussis, or whooping cough, is an infectious disease that is caused by Bordetella pertussis, affects all age groups and is vaccine preventable. Recently, an increase in reported cases of pertussis in adolescents and adults has been noted in many countries despite high immunisation rates in children. Today pertussis outnumbers all other paediatric vaccine-preventable diseases in some countries. This observation can best be explained by an increased awareness of the disease, the availability of new diagnostic tests and, perhaps, suboptimal efficacy of some pertussis vaccines. In general, B. pertussis infections in adolescents and adults are of concern as they are the most important source of transmission of B. pertussis infections to young, unprotected infants. Many studies with diphtheria and tetanus toxoid, acellular pertussis component combination vaccines, specifically designed for use in adolescents and adults, have been performed and excellent tolerability and immunogenicity have been demonstrated. With the availability of two such products, booster doses in adolescents have been introduced in Canada, Austria, Australia, France, Germany and the US, and many other countries are considering similar expansion of their immunisation programmes at present. In addition, universal immunisation of adults (Austria, every 10 years) or targeting high risk groups (e.g., parents of newborns and other care-givers to children; Germany) have been recommended. If lifelong regular booster doses against pertussis were to be recommended and universal implementation was obtained, the authors believe that the morbidity of pertussis and its spread to infants can be dramatically reduced, and it is possible that the circulation of B. pertussis could be eliminated.

Postinfectious cough: ACCP evidence-based clinical practice guidelines

BACKGROUND

Patients who complain of a persistent cough lasting >3 weeks after experiencing the acute symptoms of an upper respiratory tract infection may have a postinfectious cough. Such patients are considered to have a subacute cough because the condition lasts for no >8 weeks. The chest radiograph findings are normal, thus ruling out pneumonia, and the cough eventually resolves, usually on its own. The purpose of this review is to present the evidence for the diagnosis and treatment of postinfectious cough, including the most virulent form caused by Bordetella pertussis infection, and make recommendations that will be useful for clinical practice.

METHODS

Recommendations for this section of the guideline were obtained from data using a National Library of Medicine (PubMed) search dating back to 1950, which was performed in August 2004, of the literature published in the English language. The search was limited to human studies, using the search terms "cough," "postinfectious cough," "postviral cough," "Bordetella pertussis," "pertussis infection," and "whooping cough."

RESULTS

The pathogenesis of the postinfectious cough is not known, but it is thought to be due to the extensive inflammation and disruption of upper and/or lower airway epithelial integrity. When postinfectious cough emanates from the lower airway, this is often associated with the accumulation of an excessive amount of mucus hypersecretion and/or transient airway and cough receptor hyperresponsiveness; all may contribute to the subacute cough. In these patients, the optimal treatment is not known. Except for bacterial sinusitis or early on in a B pertussis infection, therapy with antibiotics has no role, as the cause is not bacterial infection. The use of inhaled ipratropium may be helpful. Other causes of postinfectious cough are persistent inflammation of the nose and paranasal sinuses, which leads to an upper airway cough syndrome (previously referred to as postnasal drip syndrome), and gastroesophageal reflux disease, which may be a complication of the vigorous coughing. One type of postinfectious cough that is particularly virulent is that caused by B pertussis infection. When the cough is accompanied by paroxysms of coughing, posttussive vomiting, and/or an inspiratory whooping sound, the diagnosis of a B pertussis infection should be made unless another diagnosis is proven. This infection is highly contagious but responds to antibiotic coverage with an oral macrolide when administered early in the course of the disease. A safe and effective vaccine to prevent B pertussis is now available for adults as well as children. It is recommended according to CDC guidelines.

CONCLUSIONS

In patients who have a cough lasting from 3 to 8 weeks with normal chest radiograph findings, consider the diagnosis of postinfectious cough. In most patients, a specific etiologic agent will not be identified, and empiric therapy may be helpful. A high degree of suspicion for cough due to B pertussis infection will lead to earlier diagnosis, patient isolation, and antibiotic treatment.

Conduite à tenir devant un ou plusieurs cas de coqueluche

The evolution of the epidemiology of pertussis, new licensed macrolides and vaccines, new recommendations for vaccination among adolescents and adults need an update of the French guidelines for prevention of the disease around one or grouped cases of the disease. A particular attention should be raised to the diagnosis of whooping cough in adults who are presently the main reservoir of Bordetella pertussis. Whooping cough in adults presents as an unexplained prolonged cough with nocturnal exacerbation witch accounts for most of the contaminations of young infants. A bacteriological confirmation of pertussis should be provided before implementation of preventive measures: culture and PCR are presently the gold standard for the diagnosis of pertussis in infants, children and even adults who have been coughing for less than 20 days. Later on, serology (Elisa, immuno-empreinte) is the only technique available, but cannot be interpreted if the patient has been vaccinated less than one year ago. Infants under three months should be admitted to hospital and every case submitted to respiratory isolation. Eviction from the community should be pronounced within the five first days following the onset of an effective antibiotic treatment. New macrolides should be favoured: clarithromycin for seven days or azithromycin for five days. Household contacts should be given the same prophylactic antibiotic treatment: children and adolescent not correctly immunized, parents of the index case as adults parents of not or not completely immunized infants. The vaccination program of the household should be updated. The same measures should be applied in case of grouped cases (at least two contemporary or consecutive cases in the same area). In that case, the Public Health System doctors should be involved in the investigation and the classification of the cases. The close contacts not or not completely immunized should be prescribed and antibiotic prophylaxis and an update of their vaccination program. Among the occasional contacts, high-risk people only should be treated. In the day care centres an antibiotic prophylaxis should be given to children who have received less than four vaccine shots against pertussis and to the personnel contact to the cases as well. In the schools, the antibiotic prophylaxis should be prescribed to all children of the classroom(s) not completely vaccinated and to the teacher(s) as well. In the boarding schools and institutions with handicapped children, antibiotic prophylaxis could be applied to every member if the pertussis vaccine coverage is at less than 50%. In hospitals, coughing personnel should wear masks and investigations towards pertussis should be performed in people with a more than seven day unexplained cough. Preventive measures should be applied in case of confirmation of pertussis.

Use of antibiotics in the prevention and treatment of pertussis

Antibiotics are commonly used for treating confirmed cases of pertussis and also for disease prevention in outbreak situations, and there is little evidence of antibiotic resistance of Bordetella pertussis. The most commonly used antibiotic is erythromycin, but the associated side effects limit compliance and therefore efficacy. Other antibiotics, such as clarithromycin and azithromycin, have been shown to be at least as effective as erythromycin in preventing and treating pertussis, and they also have fewer side effects, which improves compliance. This article outlines the use of different antibiotics in pertussis management and their effect on preventing disease transmission and reducing disease severity and duration.

Antibiotics for whooping cough (pertussis)

BACKGROUND

Whooping cough is a highly contagious disease. Infants are the population at highest risk of severe disease and death. Erythromycin for 14 days is recommended for treatment and contact prophylaxis but this regime is considered inconvenient and prolonged. The value of contact prophylaxis is uncertain.

OBJECTIVES

To study the benefits and risks of antibiotic treatment of and contact prophylaxis against whooping cough.

SEARCH STRATEGY

The Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 1, 2004); MEDLINE (January 1966 to February 2004); EMBASE (January 1974 to August 2003); conference abstracts and reference lists of articles were searched. Study investigators and pharmaceutical companies were approached for additional information (published or unpublished studies). There were no constraints based on language or publication status.

SELECTION CRITERIA

All randomised and quasi-randomised controlled trials of antibiotics for treatment of and contact prophylaxis against whooping cough were included in the systematic review.

DATA COLLECTION AND ANALYSIS

At least three reviewers independently extracted data and assessed the quality of each trial.

MAIN RESULTS

Twelve trials with 1,720 participants met the inclusion criteria. Ten trials investigated treatment regimens and two investigated prophylaxis regimens. The quality of the trials was variable. Results showed that short-term antibiotics (azithromycin for three days, clarithromycin for seven days, or erythromycin estolate for seven days) were equally effective with long-term antibiotic treatment (erythromycin estolate or erythromycin for 14 days) in the microbiological eradication of Bordetella pertussis (B. pertussis) from the nasopharynx. The relative risk (RR) was 1.02 (95% confidence interval (CI) 0.98 to 1.05). Side effects were fewer with short-term treatment (RR 0.66; 95% CI 0.52 to 0.83). There were no differences in clinical improvement or microbiological relapse between short and long-term treatment regimens. Contact prophylaxis (of contacts older than six months of age) with antibiotics did not significantly improve clinical symptoms or the number of cases that developed culture positive B. pertussis.

AUTHORS' CONCLUSIONS

Antibiotics are effective in eliminating B. pertussis from patients with the disease, rendering them non-infectious, but do not alter the subsequent clinical course of the illness. Effective regimens include: three days of azithromycin, seven days of clarithromycin, seven or 14 days of erythromycin estolate, and 14 days of erythromycin ethylsuccinate. Considering microbiological clearance and side effects, three days of azithromycin or seven days of clarithromycin are the best regimens. Seven days of trimethoprim/sulfamethoxazole also appeared to be effective for the eradication of B. pertussis from the nasopharynx and may serve as an alternative antibiotic treatment for patients who cannot tolerate a macrolide. There is insufficient evidence to determine the benefit of prophylactic treatment of pertussis contacts.

Unsuspected neonatal killers in emergency medicine

A neonate presenting to the emergency department can present a challenge to even the most experienced clinician. This article has focused on four deceiving and potentially devastating neonatal diseases. 1. Neonatal herpes is a potentially devastating illness without pathognomonic signs or symptoms. Early recognition and therapy can reduce mortality markedly. Although no specific sign or symptom is diagnostic,the diagnosis should be strongly considered in the presence of HSV risk factors, atypical sepsis, unexplained acute hepatitis, or focal seizure activity. Acyclovir therapy should be initiated before viral dissemination or significant CNS replication occurs. 2. Pertussis is a disease in which infants are at greatest risk of death or severe complication. Neonatal pertussis often presents in an atypical manner, lacking the classic signs and symptoms such as the "whoop."More common signs and symptoms include cough, feeding difficulty,low-grade fever, emesis, increasing respiratory distress, apnea, cyanosis,and seizures. Management should include hospitalization, supportive care, and antibiotics. 3. Congenital heart defects, particularly ductal-dependent lesions, may have an initial asymptomatic period that culminates in a rapidly progressive and fatal course. A neonate with CHD presents with shock refractory to volume resuscitation or pressor support. Resuscitative efforts are ineffective unless PGE, is administered. 4. Inborn errors of metabolism often are unsuspected because of their protean and heterogeneous nature. Signs and symptoms are subtle,are nonspecific, and often mimic other, more common diseases.An elevated index of suspicion, along with application and correct interpretation of a select few laboratory tests, is the key to making a diagnosis. Therapy is relatively straightforward and focused on resuscitation followed by prevention of catabolism and correction of specifically identified abnormalities. Although these disorders are relatively uncommon, prompt diagnosis and therapy can lead to a decrease in morbidity and mortality. The key is to maintain a high index of suspicion.

Pertussis: persistent pathogen, imperfect vaccines

Routine use of pertussis vaccines has diminished the incidence of this disease but has not eliminated the pathogen. Pertussis remains a significant cause of disease in both very young infants and in the adolescent and adult populations. Acellular pertussis vaccines have fewer adverse reactions compared with whole-cell pertussis vaccines. Although efficacious against severe disease, current vaccines may not be as efficacious against milder forms of infection. New methodologies for understanding disease pathogenesis, immune responses and vaccine development are needed to effectively interrupt continued transmission of this pathogen.

Efficacy and safety of clarithromycin versus erythromycin for the treatment of pertussis: a prospective, randomized, single blind trial

BACKGROUND

Pertussis is still a prevalent public health problem, and antibiotic therapy may decrease disease severity and limit communicability. Erythromycin is the recommended antibiotic for treatment and prophylaxis of pertussis; however, side effects of erythromycin limit its usefulness in some patients. Clarithromycin, a newer macrolide, has good in vitro activity against Bordetella pertussis and a better side effect profile.

GOALS OF THE STUDY

To compare the microbiologic and clinical efficacy and the clinical safety of a 7-day course of clarithromycin vs. a 14-day course of erythromycin in children with pertussis.

DESIGN

Prospective, randomized, single blind (investigator), parallel group trial.

METHODS

Children from 1 month to 16 years of age presenting with a clinically defined pertussis syndrome were eligible for the study. After obtaining informed written consent, we randomized patients to receive either clarithromycin (7.5 mg/kg/dose twice a day for 7 days) or erythromycin (13.3 mg/kg/dose three times a day for 14 days). Nasopharyngeal cultures for B. pertussis were performed at enrollment and after end of treatment. Clinical assessments were performed at enrollment, at end of treatment and at a 1-month follow-up visit. Adverse event data were collected throughout the study.

RESULTS

The clarithromycin (n = 76) and erythromycin (n = 77) groups were well-matched for age and previous pertussis immunization. Microbiologic eradication and clinical cure rates were 100% (31 of 31) for clarithromycin and 96% (22 of 23) for erythromycin. The clarithromycin group had significantly fewer adverse events [45% (34 of 76) for clarithromycin vs. 62% (48 of 77) for erythromycin; P = 0.035], and compliance with the medication regimen was significantly higher in these patients.

CONCLUSIONS

A 7-day regimen of clarithromycin and a 14-day course of erythromycin were equally effective for treatment of pertussis. Clarithromycin was better tolerated than conventional erythromycin therapy.

Multicenter, randomized, double-blind comparison of erythromycin estolate versus amoxicillin for the treatment of acute otitis media in children. AOM Study Group

Erythromycin is frequently prescribed in Germany for acute otitis media, but well-designed clinical trials under present epidemiological conditions are lacking. Therefore, a double-blind, randomized, multicenter trial was performed to compare the clinical efficacy and safety of erythromycin estolate versus amoxicillin in children with acute otitis media and to identify the risk factors associated with clinical failure. Investigators from 19 centers throughout Germany recruited 302 children with clinical, otoscopic, and tympanometric evidence of acute otitis media. In a double-blind fashion, patients were allocated randomly to a 10-day course of erythromycin estolate at 40 mg/kg/day in two divided doses or amoxicillin at 50 mg/kg/day in two divided doses. Clinical examinations, otoscopy, and tympanometry were performed at baseline, day 3-5, day 9-11, and at 5 weeks. Clinical outcome was assessed on day 9-11. Two-hundred eighty children were evaluable for efficacy (erythromycin group, 141; amoxicillin group, 139). Both groups were comparable with respect to demographic data and severity of disease at entry. Treatment was successful in 94% of the erythromycin-treated patients and in 96% of the amoxicillin-treated patients. Clinical outcome was statistically equivalent between groups within a range of 7 percentage points. Clinical recurrence was seen in eight erythromycin-treated children (5.7%) and in seven amoxicillin-treated children (5.0%) (P=0.81). Patients with bilateral disease at entry were at higher risk of unfavourable outcome, whereas age and presence/absence of otorrhea at entry were not associated with outcome. Treatment-related adverse events were recorded in eight (5.3%) of 151 erythromycin-treated patients and in 11 (7.3%) of 151 amoxicillin-treated patients. In this study in an outpatient setting in Germany, erythromycin estolate was as safe and effective as amoxicillin in the treatment of acute otitis media. Both drugs can be administered in a convenient twice-daily dosage schedule.

Seven days of erythromycin estolate is as effective as fourteen days for the treatment of Bordetella pertussis infections

OBJECTIVE AND METHODS

Although 14 days of erythromycin is recommended for the treatment of Bordetella pertussis infection, there have been no prospective controlled studies to support the contention that this long course of therapy is required to eradicate the microorganism from the nasopharynx or to prevent bacteriological relapse. We randomly allocated children and adults with culture-positive community-acquired pertussis to either 7 or 14 days of erythromycin estolate treatment (40 mg/kg/d; maximum dose 1 g/d). Nasopharyngeal aspirate cultures were obtained by study nurses during home visits before and at the end of treatment, and 1 week after the completion of treatment. B pertussis-specific antibodies were measured before treatment and 1 month later. Information about clinical symptoms, adverse reactions, and compliance were collected at each scheduled contact.

RESULTS AND CONCLUSIONS

A total of 168 participants were eligible for analysis (74 treated for 7 days and 94 treated for 14 days). Bacteriological persistence (positive end of therapy culture) occurred once in each group, and bacteriological relapse (positive culture 1 week after completion of treatment) occurred in one participant treated for 7 days. The overall failure rate (persistence plus relapse) of 2.70% in the 7-day group was not different than the rate of 1.06% in the 14-day group. The study had a power of 99.99% at the 5% level to detect a difference in failure rates of 10% and a power of 80% to detect a difference of 5%. We conclude that 7 days of erythromycin estolate is as effective as 14 days for the eradication of B pertussis.

Pertussis in primary care practice. Recent advances in diagnosis, treatment, and prevention

Pertussis continues to be an important vaccine-preventable disease. The recent multiple outbreaks of pertussis have heightened interest in its diagnosis, treatment, and prevention. Diagnosis remains challenging, although new diagnostic tests, including enzyme-linked immunosorbent assay of sera and polymerase chain reaction of nasopharyngeal aspirates, offer the possibility of more rapid diagnosis. Erythromycin remains the preferred antimicrobial to reduce secondary transmission of pertussis. The recent approval of acellular pertussis vaccine for the primary series of immunizations ushers in an exciting new era of pertussis prevention.

Detection of Bordetella pertussis by polymerase chain reaction and culture in the nasopharynx of erythromycin-treated infants with pertussis

BACKGROUND

Pertussis is a highly contagious respiratory disease and the most serious effects occur in young infants. Recently it has been shown that rapid and highly specific PCR can be a useful diagnostic tool for detection of pertussis infection. To our knowledge there are no previous studies concerning the disappearance of Bordetella pertussis DNA from the nasopharynx during antimicrobial treatment.

METHODS

We studied prospectively how rapidly live B. pertussis organisms and DNA of these bacteria disappear from the nasopharynx during erythromycin therapy in unvaccinated infants. Eighty-five nasopharyngeal swabs obtained from nine erythromycin-treated infants with pertussis on consecutive days during hospitalization were tested by PCR and culture. The PCR products were further analyzed by Southern hybridization.

RESULTS

On the fourth day of treatment 56% of the samples were positive by culture and 89% by PCR, whereas after 7 days the rates were 0 and 56%, respectively. In seven of nine patients PCR remained positive for 1 to 7 days longer than culture. The follow-up study also showed the semiquantitative nature of the PCR assay. The intensity of the PCR products in agarose gel usually weakened with time during erythromycin therapy.

CONCLUSIONS

The results of this study show that PCR assay can achieve the specific diagnosis of pertussis infection in a large proportion of infants even when antimicrobial treatment has killed the organisms and culture is no longer positive.