Comparison of PCR, culture, and direct fluorescent-antibody testing for detection of Bordetella pertussis

Can Comprehensive Respiratory Pathogen Panels be Used to Exclude Pertussis Infection?

BACKGROUND

Pertussis is a serious public health concern and accurate diagnosis is imperative. Comprehensive, multiplex respiratory pathogen polymerase chain reaction (PCR) panels (RPPs) have recently become popular, but their utility in excluding pertussis infection has not been fully explored.

OBJECTIVES

To determine RPP testing results for pertussis using frozen banked samples that previously tested positive on dedicated Bordetella pertussis PCR testing, and to describe positive test rates for other respiratory pathogens on these samples via RPP.

METHODS

Our microbiology laboratory retrieved banked nasopharyngeal samples from inpatient, ambulatory, and emergency department sources that were positive for pertussis using B. pertussis PCR testing from March 2015 to October 2017. RPP was performed on thawed, archived samples. Rate of pertussis identification on RPP was determined, and positive tests for other pathogens were tabulated.

RESULTS

A total of 3482 specimens were submitted for pertussis PCR testing during the study period. Of those, 138 (4%) were positive for B. pertussis, and 102 (74%) samples were banked and available for RPP testing. Fifty-seven of 102 (56%) of the banked samples had positive RPP testing for pertussis. Of the 45 samples negative for pertussis on RPP testing, 20 (44%) tested positive for other respiratory pathogens.

CONCLUSION

Negative testing for B. pertussis and positive testing for other respiratory pathogens on RPP was common in samples that previously tested positive on dedicated B. pertussis PCR testing, both of which could lead to missed diagnoses of pertussis infection. Clinicians should consider using dedicated pertussis PCR testing if pertussis infection is suspected.

Spatio-temporal comparison of pertussis outbreaks in Olmsted County, Minnesota, 2004-2005 and 2012: a population-based study

OBJECTIVE

Two pertussis outbreaks occurred in Olmsted County, Minnesota, during 2004-2005 and 2012 (5-10 times higher than other years), with significantly higher incidence than for the State. We aimed to assess whether there were similar spatio-temporal patterns between the two outbreaks.

SETTING

Olmsted County, Minnesota, USA PARTICIPANTS: We conducted a population-based retrospective cohort study of all Olmsted County residents during the 2004-2005 and 2012 outbreaks, including laboratory-positive pertussis cases.

PRIMARY OUTCOME MEASURE

For each outbreak, we estimated (1) age-specific incidence rate using laboratory-positive pertussis cases (numerator) and the Rochester Epidemiology Project Census (denominator), a medical record-linkage system for virtually all Olmsted County residents, and (2) pertussis case density using kernel density estimation to identify areas with high case density. To account for population size, we calculated relative difference of observed density and expected density based on age-specific incidence.

RESULTS

We identified 157 and 195 geocoded cases in 2004-2005 and 2012, respectively. Incidence was the highest among adolescents (ages 11 to <14 years) for both outbreaks (9.6 and 7.9 per 1000). The 2004-2005 pertussis outbreak had higher incidence in winter (52% of cases) versus summer in 2012 (53%). We identified a consistent area with higher incidence at the beginning (ie, first quartile) of two outbreaks, but it was inconsistent for later quartiles. The relative difference maps for the two outbreaks suggest a greater role of neighbourhood population size in 2012 compared with 2004-2005.

CONCLUSIONS

Comparing spatio-temporal patterns between two pertussis outbreaks identified a consistent geographical area with higher incidence of pertussis at the beginning of outbreaks in this community. This finding can be tested in future outbreaks, and, if confirmed, can be used for identifying epidemiological risk factors clustered in such areas for geographically targeted intervention.

Emergence of Bordetella holmesii as a Causative Agent of Whooping Cough, Barcelona, Spain

We describe the detection of Bordetella holmesii as a cause of whooping cough in Spain. Prevalence was 3.9% in 2015, doubling to 8.8% in 2016. This emergence raises concern regarding the contribution of B. holmesii to the reemergence of whooping cough and the effectiveness of the pertussis vaccine.

Bordetella holmesii: Still Emerging and Elusive 20 Years On

Since the first description of Bordetella holmesii in 1995, almost 100 publications have contributed to the increasing knowledge of this emerging bacterium. Although first reported to induce bacteremia mainly in immunocompromised patients, it has also been isolated in healthy persons and has shown the capacity to induce pertussis-like symptoms and other clinical entities, such as meningitis, arthritis, or endocarditis. Respiratory diseases are generally less severe than those induced by Bordetella pertussis. However, B. holmesii was found to have a higher capacity of invasiveness given the various infection sites in which it was isolated. The diagnosis is difficult, particularly as it is a slow-growing organism but also because respiratory infections are systematically misdiagnosed as B. pertussis. Treatment is delicate, as its susceptibility to macrolides (prescribed in respiratory infections) and ceftriaxone (used in invasive disease) is challenged. Regarding prevention, there is no consensus on prophylactic treatment following index cases and no vaccine is available. Epidemiological data are also sparse, with few prevalence studies available. In this chapter, we provide an overview of the current state of knowledge on B. holmesii.

Antimicrobial Susceptibility and Molecular Detection of Pertactin-producing and Pertactin-Deficient Bordetella pertussis

Resurgence of Bordetella pertussis in recent years in the United States has coincided with a dramatic rise in pertactin-deficient strains. Limited data exist on detectability by nucleic acid amplification testing and antimicrobial susceptibility of pertactin-deficient B. pertussis. This study compares 15 pertactin-producing and 15 pertactin-deficient B. pertussis isolates. Pertactin-producing and pertactin-deficient strains were equally detected by nucleic acid amplification testing and were susceptible to antibiotics.

The pertussis enigma: reconciling epidemiology, immunology and evolution

Pertussis, a highly contagious respiratory infection, remains a public health priority despite the availability of vaccines for 70 years. Still a leading cause of mortality in developing countries, pertussis has re-emerged in several developed countries with high vaccination coverage. Resurgence of pertussis in these countries has routinely been attributed to increased awareness of the disease, imperfect vaccinal protection or high infection rates in adults. In this review, we first present 1980-2012 incidence data from 63 countries and show that pertussis resurgence is not universal. We further argue that the large geographical variation in trends probably precludes a simple explanation, such as the transition from whole-cell to acellular pertussis vaccines. Reviewing available evidence, we then propose that prevailing views on pertussis epidemiology are inconsistent with both historical and contemporary data. Indeed, we summarize epidemiological evidence showing that natural infection and vaccination both appear to provide long-term protection against transmission and disease, so that previously infected or vaccinated adults contribute little to overall transmission at a population level. Finally, we identify several promising avenues that may lead to a consistent explanation of global pertussis epidemiology and to more effective control strategies.

Direct Detection of Bordetella pertussis and Bordetella parapertussis: Comparison of Polymerase Chain Reaction and Culture

We evaluated the diagnostic performance of a genomic DNA amplification method for Bordetella pertussis and Bordetella parapertussis compared with culture isolation. Aliquots from B. pertussis and B. parapertussis cultures were added to sterile physiological saline or sterile distilled water to give bacterial suspensions of 108 cells/ml and serial dilutions were prepared. Suspensions in physiological saline were cultured on charcoal agar medium; bacterial growth was observed up to dilutions of 10−7. Suspensions in distilled water were subjected to DNA extraction and nested polymerase chain reaction (PCR) was performed on the extracts; the PCR was positive up to dilutions of 10−8 for B. pertussis and 10−9 for B. parapertussis. Since the efficacy of culture isolation, regarded as the standard for the detection of B. pertussis and B. parapertussis, declines after the first stage of pertussis or with prior vaccination or antibiotic therapy, PCR, although not yet standardized, may provide an alternative diagnostic tool.

Protecting Newborns Against Pertussis: Treatment and Prevention Strategies

Pertussis is a potentially severe respiratory disease, which affects all age groups from young infants to older adults and is responsible for an estimated 195,000 deaths occurred globally in 2008. Active research is ongoing to better understand the pathogenesis, immunology, and diagnosis of pertussis. For diagnosis, molecular assays (e.g., polymerase chain reaction) for detection of Bordetella pertussis have become more widely available and support improved outbreak detection. In children, pertussis vaccines have been incorporated into routine immunization schedules and deployed for pertussis outbreak control. Lower levels of vaccine coverage are now being observed in communities where vaccine hesitancy is rising. Additionally, recognition that newborn babies are at risk of pertussis in the USA and UK has led to recommendations to immunize pregnant women. Among adolescents and older adults in the USA, Tetanus Toxoid, Reduced Diphtheria Toxoid and Acellular pertussis (Tdap) Vaccines are recommended, but substantial individual- and system-level barriers exist that will make achieving national Healthy People 2020 targets for immunization challenging. Current antimicrobial regimens for pertussis are focused on reducing the severity of disease, reducing rates of sequelae, and minimizing transmission of infection to susceptible individuals. Continued surveillance for pertussis will be important to identify opportunities for reducing young infants' exposure and reducing the impact of outbreaks among school-aged children. Laboratory-based surveillance for newly emerging strains of B. pertussis will be important to identify strains that may evade protection elicited by currently available vaccines. Efforts to develop new-generation pertussis vaccines should be considered now in anticipation of vaccine development programs, which may require ten or more years to deliver a licensed vaccine.

Predictors of Pertussis Polymerase Chain Reaction Positive Results in Minnesota, 2005-2009

Predictors of polymerase chain reaction (PCR) positivity for pertussis were assessed using Minnesota active surveillance data. Report of an exposure to pertussis and testing within the optimal time frame of ≤2 weeks were significantly associated with testing PCR positive, emphasizing the importance of asking about epidemiological factors when assessing patients for pertussis, and timely PCR testing.

Laboratory Diagnosis of Pertussis

The introduction of vaccination in the 1950s significantly reduced the morbidity and mortality of pertussis. However, since the 1990s, a resurgence of pertussis has been observed in vaccinated populations, and a number of causes have been proposed for this phenomenon, including improved diagnostics, increased awareness, waning immunity, and pathogen adaptation. The resurgence of pertussis highlights the importance of standardized, sensitive, and specific laboratory diagnoses, the lack of which is responsible for the large differences in pertussis notifications between countries. Accurate laboratory diagnosis is also important for distinguishing between the several etiologic agents of pertussis-like diseases, which involve both viruses and bacteria. If pertussis is diagnosed in a timely manner, antibiotic treatment of the patient can mitigate the symptoms and prevent transmission. During an outbreak, timely diagnosis of pertussis allows prophylactic treatment of infants too young to be (fully) vaccinated, for whom pertussis is a severe, sometimes fatal disease. Finally, reliable diagnosis of pertussis is required to reveal trends in the (age-specific) disease incidence, which may point to changes in vaccine efficacy, waning immunity, and the emergence of vaccine-adapted strains. Here we review current approaches to the diagnosis of pertussis and discuss their limitations and strengths. In particular, we emphasize that the optimal diagnostic procedure depends on the stage of the disease, the age of the patient, and the vaccination status of the patient.

Pertussis in the newborn: certainties and uncertainties in 2014

Bordetella pertussis infection remains a serious potential health risk to infants, specially in those too young to be vaccinated. Over the recent years, numerous sources highlighted a widespread resurgence, making it, again, a challenging disease. Globally, pertussis is ranked among the 10 leading causes of childhood mortality. This review summarizes the most recent literature and will address the most important aspects that pediatricians and neonatologists must be familiar with, when treating a newborńs pertussis infection.

Diagnosis of pertussis using nasopharyngeal IgA and polymerase chain reaction in specimens from outpatients in Australia

We assessed IgA antibodies and polymerase chain reaction (PCR) for diagnosis of pertussis in nasopharyngeal aspiration (NPA) samples from outpatients in Australia.   A total of 1700 patients (849 adults, 851 children) from Western Australia and the Northern Territory fulfilled the laboratory case definition for pertussis between 2004 and 2013: 732 specimens were positive by NPA IgA alone, 559 by PCR alone, and 409 by both tests. Overall, 968 cases (56.8%) were positive by PCR and 1141 cases (67.2%) by IgA [p < 0.00025]. Among pediatric patients, PCR was positive in 524 (61.3%) and IgA in 569 (67%). In 849 adult cases, the respective proportions were 52.3% and 67.4% [p < 0.00025].   The duration of cough in 507 patients was shorter in 262 pediatric cases (mean, 2.51 weeks; standard deviation [SD], 2.25) than 245 adult patients (3.27 weeks; SD, 2.79) [p = 0.0009]. PCR positivity showed a season-dependent variance (range, 5.6 to 85.9%) and peaked in the second week (71.7%) of illness. IgA antibodies peaked in the fifth week (89.5%) postinfection, and the positivity rate for NPA IgA was less variable (range, 38.3-97.2%).   Nasopharyngeal Bordetella pertussis-specific IgA antibodies are valuable in diagnosis of pertussis in Australia. Reliance on PCR alone misses a significant proportion of pertussis cases, especially those with a delayed presentation.

Epidemiological aspects of pertussis among adults and adolescents in a Korean outpatient setting: a multicenter, PCR-based study

Epidemiological data of Bordetella pertussis infection among adolescents and adults are limited in Korea. Patients (≥ 11 yr of age) with a bothersome cough for less than 30 days were enrolled during a 1-yr period at 22 hospitals in Korea. Nasopharyngeal swabs were collected for polymerase chain reaction (PCR) and for bacteriologic culture. In total, 490 patients were finally enrolled, and 34 (6.9%) patients tested positive for B. pertussis; cough duration (14.0 days [7.0-21.0 days]) and age distribution were diverse. The incidence was the highest in secondary referral hospitals, compared to primary care clinics or tertiary referral hospitals (24/226 [10.6%] vs. 3/88 [3.4%] vs. 7/176 [4.0%], P = 0.012), and the peak incidence was observed in February and August (15.8% and 15.9%), with no confirmed cases between March and June. In the multivariate analysis, post-tussive vomiting was significantly associated with pertussis (odds ratio, 2.508; 95% confidence interval, 1.146-5.486) and secondary referral hospital showed a borderline significance. In conclusion, using a PCR-based method, 6.9% of adolescent and adult patients with an acute cough illness had pertussis infection in an outpatient setting. However, hospital levels and seasonal trends must be taken into account to develop a better strategy for controlling pertussis.

Evaluation of 3 analyte-specific reagents for detection of Bordetella pertussis and Bordetella parapertussis in clinical specimens

The performance of 3 analyte-specific reagents (ASRs), Elitech Biosciences, EraGen Biosciences, and Focus Diagnostic, was evaluated for detection of Bordetella pertussis (BP) and Bordetella parapertussis (BPP) in nasopharyngeal swab specimens. A total of 104 frozen, leftover clinical specimens obtained from pediatric patients during 2011-2012 were included in this study. Performance was compared to the Bordetella real-time polymerase chain reaction (PCR) laboratory-developed test (LDT). The positive percent agreement for detection of BP by Elitech was 96% (95% confidence interval [CI]: 85.14-99.30); EraGen and Focus was 98% (95% CI: 87.99-99.89) in comparison to LDT PCR assay. The negative percent agreement of Elitech, EraGen, and Focus in comparison to LDT was 96% (95% CI: 85.14-99.30), 92% (95% CI: 79.89-97.41), and 96% (95% CI: 85.14-99.30), respectively. Limit of detection (LOD) for BP was 0.1 CFU/reaction by both Focus and EraGen and 1.0 CFU/reaction by Elitech. However, LOD for BPP was lower by EraGen (0.1 CFU/reaction) compared to Focus (1.0 CFU/reaction) and Elitech (1.0 CFU/reaction). These results demonstrate that all 3 ASRs tested are comparable and reliable for routine clinical diagnosis of pertussis and parapertussis.

Neonatal pertussis, cocooning and maternal immunization

The rising incidence of whooping cough, a highly contagious infection caused by Bordetella pertussis, is particularly significant for young infants who have the highest risk for morbidity and mortality. The pertussis resurgence has led to a shift in primary prevention relying on childhood vaccination to a cocooning strategy, that is, vaccination of close contacts of newborn infants (new mothers, fathers, grandparents, siblings, caretakers, etc.), thereby reducing pertussis exposure. Immunization of women during pregnancy rather than during the immediate postpartum period (the initial cocooning recommendation) appears to be a better approach by directly providing protection through transplacental transfer of maternal vaccine-induced antibodies. This article describes neonatal pertussis, cocooning as a means of reducing neonatal exposure to pertussis and maternal immunization as a means of protecting young infants against pertussis infection.

Multiplex real-time PCR assay for detection and differentiation of Bordetella pertussis and Bordetella parapertussis

BACKGROUND AND OBJECTIVE

Rapid diagnosis of pertussis is important for the timely isolation of the infection source and early prevention measures among the contact persons, especially among non-vaccinated infants for whom pertussis is life-threatening.

MATERIALS AND METHODS

Targets IS481, IS1001, BP0026 and human GAPDH gene were used to develop a multiplex real-time PCR assay based on the TaqMan technology for detection and identification of Bordetella pertussis and Bordetella parapertussis in clinical samples. A total of 121 human clinical specimens obtained within 2012-2013 were used to evaluate the multiplex real-time PCR assay. Clinical specimens were also tested for culture and conventional PCR. Sensitivity and specificity for culture, conventional PCR, and multiplex real-time PCR were measured in comparison with a clinical standard for B. pertussis infection.

RESULTS

The lower limit of detection (LLOD) of the multiplex assay was similar to the LLOD of each target in an individual assay format, which was approximately 1 genomic equivalent per reaction for IS481, IS1001 and 10 genomic equivalents per reaction for BP0026 target. When the B. pertussis assays were compared with a clinical standard for B. pertussis infection, sensitivity was 5, 59 and 89% the specificity was 100, 100 and 100% for culture, conventional PCR, and multiplex real-time PCR, respectively.

CONCLUSIONS

Developed multiplex real-time PCR offers a fast tool with high sensitivity and specificity for the diagnosis of B. pertussis and B. parapertussis infections which is suitable for implementation in a routine laboratory diagnostics.

Bordetella holmesii: an under-recognised Bordetella species

Bordetella holmesii, first described in 1995, is believed to cause both invasive infections (bacteraemia, meningitis, endocarditis, pericarditis, pneumonia, and arthritis) and pertussis-like symptoms. Infection with B holmesii is frequently misidentified as being with B pertussis, the cause of whooping cough, because routine diagnostic tests for pertussis are not species-specific. In this Review, we summarise knowledge about B holmesii diagnosis and treatment, and assess research needs. Although no fatal cases of B holmesii have been reported, associated invasive infections can cause substantial morbidities, even in previously healthy individuals. Antimicrobial treatment can be problematic because B holmesii's susceptibility to macrolides (used empirically to treat B pertussis) and third-generation cephalosporins (often used to treat invasive infections) is lower than would be expected. B holmesii's adaptation to human beings is continuing, and virulence might increase, causing the need for better diagnostic assays and epidemiological surveillance.

Nosocomial pertussis in neonatal units

Pertussis remains a public health concern in many countries despite high vaccination coverage rates. Nosocomial outbreaks of pertussis continue to occur in neonatal units. Neonates and young infants admitted to neonatal intensive care units constitute a pool of susceptible high-risk patients given their prematurity, inadequate immune response and the fact that they are too young to have completed their primary vaccination series against pertussis. This article reviews nosocomial pertussis in neonates and infants, focusing on the role of healthcare workers (HCWs). Outbreaks in neonatal units are often traced to HCWs and are associated with serious morbidity or even a fatal outcome among susceptible young infants. A high index of suspicion is required for early recognition and isolation of patients admitted with suspected or proven pertussis, as well as for HCWs with a compatible clinical syndrome, regardless of vaccination status. Contact investigation is also essential in order to guide administration of post-exposure prophylaxis. Recommendations for a booster vaccination for HCWs are in place in several countries; however, the need of HCWs for lifelong immunity against pertussis cannot be fulfilled by the current vaccine.

Comparison of culture and real-time PCR for detection of Bordetella pertussis isolated from patients in Iran

BACKGROUND AND OBJECTIVE

Due to contagiousness of pertussis, a rapid and sensitive method for diagnosis is required to initiate the treatment and interrupt its transmission.

MATERIALS AND METHODS

To detect B. pertussis strains, we used two real-time PCR targeting IS481 and BP283 sequences and compared factors influencing culture and real-time PCR results.

RESULTS

Totally, 779 specimens were collected from patients among which 11 (1.4%) were culture positive. Using IS481 and BP283 primers, 122 (15.6%) and 100 (12.8%) were diagnosed as infected specimens respectively. There were significant relationships between the real-time PCR method for diagnosis of B. pertussis and age, sex and vaccination of patients before sampling.

CONCLUSION

The real-time PCR is superior and much more sensitive than culture for diagnosis of B. pertussis. However, the sensitivity was improved when both IS481 and BP283 were used. Correct sampling and transportation of specimen also improved the detection rate in our research.

Using a bayesian latent class model to evaluate the utility of investigating persons with negative polymerase chain reaction results for pertussis

Pertussis remains difficult to control. Imperfect sensitivity of diagnostic tests and lack of specific guidance regarding interpretation of negative test results among patients with compatible symptoms may contribute to its spread. In this study, we examined whether additional pertussis cases could be identified if persons with negative pertussis test results were routinely investigated. We conducted interviews among 250 subjects aged ≤18 years with pertussis polymerase chain reaction (PCR) results reported from 2 reference laboratories in Wisconsin during July-September 2010 to determine whether their illnesses met the Centers for Disease Control and Prevention's clinical case definition (CCD) for pertussis. PCR validity measures were calculated using the CCD as the standard for pertussis disease. Two Bayesian latent class models were used to adjust the validity measures for pertussis detectable by 1) culture alone and 2) culture and/or more sensitive measures such as serology. Among 190 PCR-negative subjects, 54 (28%) had illnesses meeting the CCD. In adjusted analyses, PCR sensitivity and the negative predictive value were 1) 94% and 99% and 2) 43% and 87% in the 2 types of models, respectively. The models suggested that public health follow-up of reported pertussis patients with PCR-negative results leads to the detection of more true pertussis cases than follow-up of PCR-positive persons alone. The results also suggest a need for a more specific pertussis CCD.

Estimating the burden of pertussis in young children on hospitals and emergency departments: a study using linked routinely collected data

Potential underestimation of the health system burden of pertussis was investigated by linking administrative datasets including pertussis notifications, hospitalizations and emergency department (ED) presentations for 1 304 876 children aged <15 years in NSW, Australia. From 2005 to 2008, 3006 children had a pertussis notification, 455 were hospitalized and 644 had an ED presentation with a coded diagnosis of pertussis. Linking hospital and ED records with pertussis notifications identified 140 hospitalizations and 735 ED presentations which occurred ± 7 days from notification but did not have a diagnosis of pertussis recorded. These additional events were more likely to have a diagnosis of bronchiolitis, upper respiratory infection and cough compared to all other admissions and presentations. Including these additional events significantly increased the proportion of notified cases that were hospitalized or visited EDs, particularly for those aged 5 to <15 years. Linked administrative data allowed more comprehensive estimation of the health system burden of pertussis.

A Multicenter Study of Pertussis Infection in Adults with Coughing in Korea: PCR-Based Study

BACKGROUND

Limited data on the incidence and clinical characteristics of adult pertussis infections are available in Korea.

METHODS

Thirty-one hospitals and the Korean Centers for Disease Control and Prevention collaborated to investigate the incidence and clinical characteristics of pertussis infections among adults with a bothersome cough in non-outbreak, ordinary outpatient settings. Nasopharyngeal aspirates or nasopharyngeal swabs were collected for polymerase chain reaction (PCR) and culture tests.

RESULTS

The study enrolled 934 patients between September 2009 and April 2011. Five patients were diagnosed as confirmed cases, satisfying both clinical and laboratory criteria (five positive PCR and one concurrent positive culture). Among 607 patients with cough duration of at least 2 weeks, 504 satisfied the clinical criteria of the US Centers for Disease Control and Prevention (i.e., probable case). The clinical pertussis cases (i.e., both probable and confirmed cases) had a wide age distribution (45.7±15.5 years) and cough duration (median, 30 days; interquartile range, 18.0~50.0 days). In addition, sputum, rhinorrhea, and myalgia were less common and dyspnea was more common in the clinical cases, compared to the others (p=0.037, p=0.006, p=0.005, and p=0.030, respectively).

CONCLUSION

The positive rate of pertussis infection may be low in non-outbreak, ordinary clinical settings if a PCR-based method is used. However, further prospective, well-designed, multicenter studies are needed.

Increased risk of pertussis in patients with asthma

BACKGROUND

The recent pertussis outbreak in California highlights the effect of pertussis on public health. In 2004, a pertussis outbreak occurred in Olmsted County, Minnesota, despite a high vaccine uptake. This outbreak provided a natural experiment to assess the relationship between asthma and pertussis.

OBJECTIVE

We sought to determine whether asthmatic subjects have a higher risk of pertussis than nonasthmatic subjects.

METHODS

We conducted a population-based case-control study. There were 223 pertussis cases identified by means of PCR in 2004 and 2005. We identified age- and sex-matched control subjects from 5537 patients with negative test results for pertussis. We conducted a comprehensive medical record review and applied predetermined criteria to ascertain asthma status. Conditional logistic regression was fit to assess the effect of asthma status on the risk of pertussis.

RESULTS

Of the 223 subjects, 164 were eligible for the study, and 328 matched control subjects (1:2 matching) were enrolled. Of these 164 subjects, 50% were male, and 82% were white. The median age at the index date of pertussis was 14 years. Sixty-two (38%) of the 164 cases had asthma before the index date of pertussis compared with 85 (26%) of the 328 control subjects (odds ratio, 1.73; 95% CI, 1.12-2.67; P = 013). The population attributable risk percentage of asthma for risk of pertussis was 17%.

CONCLUSIONS

Given the high prevalence of asthma and the ongoing risk of pertussis throughout the United States, consideration of defining asthmatic subjects as a target group for pertussis vaccination (eg, replacing decennial tetanus-diphtheria booster with tetanus, diphtheria, and acellular pertussis vaccine for adolescents and adults) should be given.

Towards improved accuracy of Bordetella pertussis nucleic acid amplification tests

In many clinical microbiology laboratories, nucleic acid amplification tests such as PCR have become the routine methods for the diagnosis of pertussis. While PCR has greatly increased the ability of laboratories to detect Bordetella pertussis infections, it has also been associated with false-positive results that can, given the tendency of B. pertussis to cause outbreaks, result in unnecessary and costly control measures. The species specificity of Bordetella gene targets and their number of copies per genome greatly impact the performance characteristics of nucleic acid amplification tests for B. pertussis. It is crucial that laboratorians recognize these characteristics, to limit false-positive test results and prevent pseudo-outbreaks.

An upsurge in pertussis: epidemiology and trends

OBJECTIVE

The objective of the study was to review the 2010 pertussis upsurge occurring within California and recent experiences at a large tertiary care children's hospital within California.

METHODS

A retrospective review of all specimens submitted for Bordetella pertussis polymerase chain reaction assay from the emergency department at a large tertiary care children's hospital from January 2009 to August 2010. Outcome measures were the number of specimens submitted, the number of positive specimens, and the percentage of positive specimens.

RESULTS

The last peak incidence of pertussis, in the Unite States, was seen in 2005 with an annual incidence of 25,616 reported cases. Comparing 2010 with 2009 during the same period, the total number of positive cases increased from 13 to 94, a 723% increase at our institution. The median monthly number of positive specimen was 1.5 for 2009 and 6.5 for 2010 (P = 0.0169).

CONCLUSIONS

Hospitals, private practitioners, and the California Department of Public Health need to emphasize prompt diagnosis and treatment of this contagious infection to limit the spread to susceptible individuals. A more widespread safe and effective vaccination program will hopefully enhance protection against pertussis infection.

The diagnosis of pertussis: which method to choose?

Despite the introduction of routine vaccination against pertussis for more than a half century, leading to a drastic decline in the number of reported cases, pertussis continues to be an important respiratory disease afflicting unvaccinated infants and previously vaccinated children as well as adults in whom immunity has waned. The diagnosis of pertussis is challenging and accurate laboratory identification of Bordetella infections remains problematic. Common laboratory diagnostic methods used for pertussis diagnosis include culture, direct-fluorescent-antibody testing (DFA), serology and polymerase chain reaction (PCR). Culture of Bordetella pertussis is highly specific but fastidious and has limited sensitivity. DFA provides a much more rapid result, but has the disadvantage of poor sensitivity and specificity. Serology is not useful in infants. In older persons, it is hampered by the limitations of paired sera and it provides mainly a retrospective diagnosis. Such limitations of conventional diagnosis testing have led to the development of PCR assays. Notwithstanding its lack of standardization, PCR has been found to be more sensitive and more specific than other methods. In this report, we aimed to review current knowledge about the available diagnostic methods and tests that accurately diagnose pertussis.

Triplex real-time PCR assay for detection and differentiation of Bordetella pertussis and Bordetella parapertussis

A triplex real-time PCR assay for detection and differentiation of Bordetella pertussis and Bordetella parapertussis was developed. Three targets were used for amplification in a single tube: the insertion sequence IS481 and the pertussis toxin promoter region (ptxP) for B. pertussis, and the insertion sequence IS1001 for B. parapertussis. The performance of this PCR assay was evaluated in parallel in three single-target real-time PCR assays using DNA extracted from B. pertussis and B. parapertussis reference strains and nasopharyngeal swabs taken from 105 patients who had been coughing for more than 7 days. The minimum detection limit of the triplex PCR was one to five colony-forming units (CFU) of B. pertussis and 1 CFU of B. parapertussis per reaction, and the coefficients of both intra- and inter-assay variation were less than 7%. Results were available within 4 h. Of the 105 nasopharyngeal samples, seven were culture positive and 23 were PCR positive for B. pertussis. All culture-positive samples were also PCR positive. Our single-tube triplex real-time PCR assay proved to be sensitive, specific and suitable for simultaneous detection and discrimination of B. pertussis and B. parapertussis.

Use of Bordetella pertussis BP3385 to establish a cutoff value for an IS481-targeted real-time PCR assay

This study utilized the Bordetella pertussis single-copy PCR target BP3385 as a means of confirming IS481 PCR-positive reactions with cycle threshold (C(T)) values of >35. IS481 PCRs with C(T) values of >35 cycles may represent PCR conditions where there is <1 CFU of B. pertussis per PCR.

Tetanus-diphtheria-acellular pertussis vaccination of adults in the USA

Pertussis is an important cause of morbidity and mortality, and its incidence has been increasing in adolescents and adults over the past two decades. Waning immunity in adolescents and adults may be partially responsible. Adults can suffer significant illness from pertussis and its complications, such as pneumonia, rib fractures and syncope. Moreover, adults serve as a source of disease for infants, who are more vulnerable to severe complications and even death. The economic burden of pertussis is substantial, in terms of both medical and nonmedical costs. Fortunately, the burden of pertussis disease can now be safely and effectively reduced by vaccinating adults with tetanus-diphtheria-acellular pertussis (Tdap) vaccine. Further research is needed to elucidate the role of vaccination in pregnant women and those over 65 years of age, and also to determine whether further booster doses of Tdap are needed.

Utility of composite reference standards and latent class analysis in evaluating the clinical accuracy of diagnostic tests for pertussis

Numerous evaluations of the clinical sensitivity and specificity of PCR and serologic assays for Bordetella pertussis have been hampered by the low sensitivity of culture, the gold standard test, which leads to biased accuracy estimates. The bias can be reduced by using statistical approaches such as the composite reference standard (CRS) (e.g., positive if culture or serology positive; negative otherwise) or latent class analysis (LCA), an internal reference standard based on a statistical model. We illustrated the benefits of the CRS and LCA approaches by reanalyzing data from a 1995 to 1996 study of cough illness among 212 patients. The accuracy of PCR in this study was evaluated using three reference standards: culture, CRS, and LCA. Using specimens obtained 0 to 34 days after cough onset, estimates of the sensitivity of PCR obtained using CRS (47%) and LCA (34%) were lower than the culture-based estimate (62%). The CRS and LCA approaches, which utilized more than one diagnostic marker of pertussis, likely produced more accurate reference standards than culture alone. In general, the CRS approach is simple, with a well-defined disease status. LCA requires statistical modeling but incorporates more indicators of disease than CRS. When three or more indicators of pertussis are available, these approaches should be used in evaluations of pertussis diagnostic tests.

Prevention of infectious diseases in athletes

The sports medicine physician may face challenging issues regarding infectious diseases when dealing with teams or highly competitive athletes who have difficulties taking time off to recover. One must treat the individual sick athlete and take the necessary precautions to contain the spread of communicable disease to the surrounding team, staff, relatives, and other contacts. This article reviews preventive strategies for infectious disease in athletes, including immunization recommendations and prophylaxis guidelines, improvements in personal hygiene and prevention of spread of infectious organisms by direct contact, insect-borne disease precautions, and prevention of sexually transmitted diseases. A special emphasis on immunizations focuses on pertussis, influenza, and meningococcal prophylaxis.

Predicting pertussis in a pediatric emergency department population

Cases of pertussis, a potentially life-threatening illness in infants younger than 6 months of age, are at a 40-year high. Children frequently present to emergency departments for initial evaluation. Quick recognition of the illness allows rapid triage, isolation, and prevention of nosocomial transmission. A retrospective, case-control chart review was conducted of pediatric emergency department patients (0 to 18 years of age) presenting between January 1, 2003, and December 31, 2004. Analysis focused on the exploration of medical history and physical examination variables as predictors using laboratory verification of the presence of pertussis as a binary outcome variable. Infants younger than 2 months who have a cough or choking associated with cyanosis, as well as a cough and rhonchi on physical examination, have a high likelihood of pertussis and should be identified in triage, isolated immediately, and tested for pertussis. This may lead to appropriate therapy for this population and decrease the transmission of pertussis to other patients and staff in the pediatric emergency department.

Limited applicability of direct fluorescent-antibody testing for Bordetella sp. and Legionella sp. specimens for the clinical microbiology laboratory

The rapid diagnosis of infections with Bordetella and Legionella species is important for patient management. With observed increases in direct fluorescent-antibody (DFA) testing volumes, we retrospectively compared the performance characteristics of DFA testing to those of culture and PCR. For Bordetella sp., samples were classified as positive by DFA testing (184 [3%] of 6,195 samples) and culture (150 [2%] of 6,251 samples) significantly less often than by PCR (2,557 [10%] of 26,929 samples). Of 360 samples tested by both DFA and PCR methods, 81 (16 by DFA testing and 79 by PCR) were determined to be positive for Bordetella, with a sensitivity and specificity of DFA testing of 18% and 99%, respectively. Of 1,426 samples tested by both DFA and culture methods, 48 (44 by DFA testing and 15 by culture) were determined to be positive for Bordetella, with a sensitivity and specificity of DFA testing of 73% and 98%, respectively. For Legionella sp., samples were identified as positive by DFA testing (31 [0.25%] of 12,597 samples) and culture (85 [0.6%] of 13,572 samples) significantly less often than by PCR (27 [4%] of 716 samples). Of 62 samples tested by both DFA and PCR methods, none were positive for Legionella sp. by DFA testing and 3 were positive by PCR. Of 3,923 samples tested by both DFA and culture methods, 22 (3 by DFA testing and 21 by culture) were positive for Legionella sp., with a sensitivity and specificity of DFA testing of 9.5% and 100%. Overall, DFA testing for Bordetella sp. and Legionella sp. is an insensitive method, and despite its continued popularity, clinical microbiology laboratories should not offer it when more sensitive tests like PCR are available.

Evaluation of Polymerase Chain Reaction and Culture for Diagnosis of Pertussis in the Control of a County-Wide Outbreak Focused among Adolescents and Adults

During a large pertussis outbreak, culture and polymerase chain reaction (PCR) were used to identify 149 case patients; of these case patients, 79 had positive PCR and culture results, 59 had positive PCR results and negative culture results, 11 had negative PCR results and positive culture results (10 PCR-negative, culture-positive specimens were collected < or = 14 days after illness onset). PCR and culture of samples obtained < or = 2 weeks after illness onset and PCR of samples obtained > 2 weeks after illness onset proved to be most diagnostically useful.

Pertussis resurgence: diagnosis, treatment, prevention, and beyond

The introduction of routine vaccination against Bordetella pertussis more than a half century ago led to a drastic decline in the number of reported cases of pertussis. It was originally believed that lifelong immunity was afforded after vaccination. Unfortunately, this belief is flawed, as the highest number of pertussis cases since 1959 was reported in 2004. This significant increase has led to additional research on immunity, vaccination, and treatment of B. pertussis in all age groups. We performed a MEDLINE search of literature from 1966-2006 to evaluate and review the existing data on immunity to and prevention or treatment of B. pertussis infections. Additional articles were identified from the bibliographies of reviewed literature. Numerous articles pertaining to these topics have been published recently. The most significant changes in the management of this infectious disease surround the new recommendations by the Advisory Committee on Immunization Practices for adult and adolescent immunizations to assist in preventing outbreaks of B. pertussis. The Centers for Disease Control and Prevention recently published guidelines updating the recommended pharmacologic agents for treatment or prevention of B. pertussis. Despite decades of successful vaccination programs, pertussis continues to be a problematic disease. Fortunately, data and vaccines are now available that make development of a pertussis booster vaccination campaign reasonable. However, until widespread compliance with such programs is achieved, clinicians need to maintain vigilance against pertussis.

Detection of respiratory pathogens by real-time PCR in children with clinical suspicion of pertussis

The use of a multiplex respiratory real-time PCR in patients clinically suspected of pertussis increases the number of pathogens detected.