Issues associated with and recommendations for using PCR to detect outbreaks of pertussis

Durability of protection after 5 doses of acellular pertussis vaccine among 5-9 year old children in King County, Washington

PURPOSE

Waning of immunity after vaccination with the acellular Pertussis (aP) vaccine has been proposed as one of the main reasons for pertussis resurgence in the US. In this study, we estimated time-varying vaccine effectiveness after 5 doses of aP vaccine.

METHODS

We conducted a retrospective cohort study among children 5-9 years old (born between 2008 and 2012) living in King County, Washington, USA, who participated in the Washington State Immunization Information System. We estimated time-varying vaccine effectiveness after 5 doses of aP using smoothed scaled Schoenfeld residuals obtained from fitting Cox proportional hazards models to the data as well as piecewise constant Poisson regression.

RESULTS

There were 55 pertussis cases in this cohort, of whom 22 (40%) were fully-vaccinated and 33 (60%) were under-vaccinated. Vaccine effectiveness (VE) remained high for up to 42 months after the fifth dose (VE(t) = 89%; 95% CI: 64%, 97%) as estimated using survival analysis methods and up to 4 years (VE(t) = 93%; 95% CI: 67%, 98%) as estimated using Poisson regression.

CONCLUSION

We did not find evidence for waning of vaccine effectiveness for up to four years after 5 doses of aP among 5 -9 years old children in King County, WA.

Association of Diphtheria-Tetanus-Acellular Pertussis Vaccine Timeliness and Number of Doses With Age-Specific Pertussis Risk in Infants and Young Children

IMPORTANCE

In most countries, the diphtheria-tetanus-acellular pertussis (DTaP) vaccine is administered as a 3-dose infant series followed by additional booster doses in the first 5 years of life. Short-term immunity from the DTaP vaccine can depend on the number, timing, and interval between doses. Not receiving doses in a timely manner might be associated with a higher pertussis risk.

OBJECTIVE

To examine the association between number and timeliness of vaccine doses and age-specific pertussis risk.

DESIGN, SETTING, AND PARTICIPANTS

This population-based, retrospective cohort study used Washington State Immunization Information System data and pertussis surveillance data from Public Health Seattle and King County, Washington. Included participants were children aged 3 months to 9 years born or living in King County, Washington, between January 1, 2008, and December 31, 2017. Data were analyzed from June 30 to December 1, 2019.

EXPOSURES

Being undervaccinated (receiving fewer than recommended doses at a given age) or delayed vaccination (not receiving doses within time frames recommended by Centers for Disease Control and Prevention).

MAIN OUTCOMES AND MEASURES

Suspected, probable, and confirmed pertussis diagnosis.

RESULTS

A total of 316 404 children (median age, 65.2 months [interquartile range, 35.3-94.1 months]; 162 025 boys [51.2%]) as of December 31, 2017, with 17.4 million person-months of follow-up were included in the analysis. A total of 19 943 children (6.3%) had no vaccines recorded in the Immunization Information System, 116 193 (36.7%) received a vaccine with a delay, and 180 268 (56.9%) were fully vaccinated with no delay. Delayed vaccination and undervaccination rates were higher for older children (17.6% delayed or undervaccinated at age 2 months for dose 1 at 3 months vs 41.6% at age 5 years for dose 5) but improved for successive birth cohorts (52.2% for 2008 birth cohort vs 32.3% for 2017 birth cohort). Undervaccination was significantly associated with higher risk of pertussis for the 3-dose primary series (adjusted relative risk [aRR], 4.8; 95% CI, 3.1-7.6), the first booster (aRR, 3.2; 95% CI, 2.3-4.5), and the second booster (aRR, 4.6; 95% CI, 2.6-8.2). However, delay in vaccination among children who received the recommended number of vaccine doses was not associated with pertussis risk.

CONCLUSIONS AND RELEVANCE

The results of this cohort study suggest that undervaccination is associated with higher pertussis risk. Short delays in vaccine receipt may be less important if the age-appropriate number of doses is administered, but delaying doses is not recommended. Ensuring that children receive all doses of pertussis vaccine, even if there is some delay, is important.

Asymptomatic Bordetella pertussis infections in a longitudinal cohort of young African infants and their mothers

Recent pertussis resurgence in numerous countries may be driven by asymptomatic infections. Most pertussis surveillance studies are cross-sectional and cannot distinguish asymptomatic from pre-symptomatic infections. Longitudinal surveillance could overcome this barrier, providing more information about the true burden of pertussis at the population level. Here we analyze 17,442 nasopharyngeal samples from a longitudinal cohort of 1320 Zambian mother/infant pairs. Our analysis has two elements. First, we demonstrate that the full range of IS481 qPCR CT values provides insight into pertussis epidemiology, showing concordance of low and high CT results over time, within mother/infant pairs, and in relation to symptomatology. Second, we exploit these full-range qPCR data to demonstrate a high incidence of asymptomatic pertussis, including among infants. Our results demonstrate a wider burden of pertussis infection than we anticipated in this population, and expose key limitations of threshold-based interpretation of qPCR results in infectious disease surveillance.

Asymptomatic Bordetella pertussis infections in young African infants and their mothers identified within a longitudinal cohort

Despite long-standing vaccination programs, pertussis incidence has increased in numerous countries; transmission by asymptomatic individuals is a suspected driver of this resurgence. However, unequivocal evidence documenting asymptomatic infections in adults and children is lacking due, in part, to the cross-sectional nature of most pertussis surveillance studies. In addition, modern pertussis surveillance relies on quantitative PCR (qPCR) using fixed diagnostic thresholds to identify cases. To address this gap, we present a longitudinal analysis of 17,442 nasopharyngeal samples collected from a cohort of 1,320 Zambian mother/infant pairs. Using full-range cycle threshold (CT) values from IS481 qPCR assays, we document widespread asymptomatic infections among mothers and also, surprisingly, among young infants. From an initial group of eight symptomatic infants who tested positive by qPCR, we identify frequent contemporaneous subclinical infections in mothers. Within the full cohort, we observe strong temporal correlation between low- and high-intensity qPCR signals. We compute a single time-averaged score for each individual summarizing the evidence for pertussis infection (EFI), and show that EFI strongly clusters within mother/infant pairs, and is strongly associated with clinical symptomatology and antibiotic use. Overall, the burden of pertussis here is substantially underestimated when restricting diagnostic criteria to IS481 CT≤35. Rather, we find that full-range CT values provide valuable insights into pertussis epidemiology in this population, and illuminate the infection arc within individuals. These findings have significant implications for quantifying asymptomatic pertussis prevalence and its contribution to overall transmission. Our results also expose limitations of threshold-based interpretations of qPCR assays in infectious disease surveillance.

Challenges and clinical relevance of molecular detection of Bordetella pertussis in South Africa

Background

We assessed the utility of a multi-target, real-time PCR assay for Bordetella pertussis detection and diagnosis in patients with severe respiratory illness (SRI), influenza-like illness (ILI), and asymptomatic controls.

Methods

Real-time PCR detection of IS481, pIS1001, hIS1001 and ptxS1 was performed on nasopharyngeal specimens (SRI, ILI and controls) and induced sputum (SRI) collected from June 2012 to May 2016 through respiratory illness surveillance. Using PCR cycle threshold (C_t) value cut-offs, IS481 positive cases were classified as confirmed (C_t < 35) or possible (C_t 35–39) pertussis disease.

Results

Among 12,922 samples, 146 (1.1%) were IS481 positive of which 62% (90/146) were classified as confirmed. The attributable fraction (AF) was 92.2% (95% CI, 65.6 to 98.2%) and 90.5% (95% CI, 57.5 to 97.9%) amongst SRI and ILI PCR-confirmed pertussis cases, respectively. Amongst possible pertussis cases, AF was 36.9% (95% CI, − 142.3 to 83.6%) and 67.5% (95% CI, − 30.6 to 91.9%) in the SRI and ILI groups, respectively.

Conclusion

All IS481 positive specimens could be considered as B. pertussis infection, and potentially pertussis disease with supportive clinical information.

Electronic supplementary material

The online version of this article (10.1186/s12879-019-3869-7) contains supplementary material, which is available to authorized users.

Pertussis outbreak in Polish shooters with adverse event analysis

In addition to different injuries, infections are the most common reason for giving up training altogether or reducing its volume and intensity, as well as a lack of opportunities to participate in sports competitions. Nowadays, a slow but constant re-emergence of pertussis, especially among teenagers and young adults, including athletes, can be observed. This paper describes an outbreak of pertussis among professional Polish shooters, focusing on the transmission of Bordetella pertussis infection between members of the national team, its influence on performance capacity and adverse event analysis. From 9 June, 2015 to 31 July, 2015, a total of 4 confirmed and suspected cases of pertussis were reported among members of the Polish Sport Shooting National Team, their relatives and acquaintances. Pertussis significantly decreased exercise performance of the first athlete, a 35-year-old woman, interrupted her training, and finally resulted in failure to win a medal or quota place. Pertussis also significantly decreased performance of the second athlete, a 25-year-old shooter. The other cases emerged in their families. Whooping cough is a real threat to athletes and should be prevented. Preventive measures include appropriate immunization, constant medical supervision, as well as early isolation, diagnostic tests and treatment of all infected sport team members. Regular administration of booster doses of the acellular pertussis vaccine (Tdpa) every 5 years seems reasonable.

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.

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.

Harmonization of Bordetella pertussis real-time PCR diagnostics in the United States in 2012

Real-time PCR (rt-PCR) is an important diagnostic tool for the identification of Bordetella pertussis, Bordetella holmesii, and Bordetella parapertussis. Most U.S. public health laboratories (USPHLs) target IS481, present in 218 to 238 copies in the B. pertussis genome and 32 to 65 copies in B. holmesii. The CDC developed a multitarget PCR assay to differentiate B. pertussis, B. holmesii, and B. parapertussis and provided protocols and training to 19 USPHLs. The 2012 performance exercise (PE) assessed the capability of USPHLs to detect these three Bordetella species in clinical samples. Laboratories were recruited by the Wisconsin State Proficiency Testing program through the Association of Public Health Laboratories, in partnership with the CDC. Spring and fall PE panels contained 12 samples each of viable Bordetella and non-Bordetella species in saline. Fifty and 53 USPHLs participated in the spring and fall PEs, respectively, using a variety of nucleic acid extraction methods, PCR platforms, and assays. Ninety-six percent and 94% of laboratories targeted IS481 in spring and fall, respectively, in either singleplex or multiplex assays. In spring and fall, respectively, 72% and 79% of USPHLs differentiated B. pertussis and B. holmesii and 68% and 72% identified B. parapertussis. IS481 cycle threshold (CT) values for B. pertussis samples had coefficients of variation (CV) ranging from 10% to 28%. Of the USPHLs that differentiated B. pertussis and B. holmesii, sensitivity was 96% and specificity was 95% for the combined panels. The 2012 PE demonstrated increased harmonization of rt-PCR Bordetella diagnostic protocols in USPHLs compared to that of the previous survey.

Diagnosis of pertussis: a historical review and recent developments

The accurate and timely diagnosis of pertussis continues to be challenging. The widespread use of pertussis vaccines has dramatically altered the epidemiology and clinical presentation of pertussis disease, such that many cases do not present with the hallmark symptoms, such as inspiratory whoop, post-tussive vomiting and paroxysmal cough. A variety of laboratory tools are available to aid in the diagnosis of pertussis, including culture, direct fluorescent antibody testing, PCR, and paired and single serology techniques. This article reviews the strengths and limitations, including the sensitivity and specificity, of each of these diagnostic tools.

Estimation of the underlying burden of pertussis in adolescents and adults in Southern Ontario, Canada

Despite highly successful vaccination programs and high vaccine uptake, both endemic pertussis and periodic pertussis outbreaks continue to occur. The under-recognized role of adolescents and adults in disease transmission, due to waning immunity following natural infection and vaccination, and reduced likelihood of correct diagnosis, may contribute to pertussis persistence. We constructed a mathematical model to describe the transmission of pertussis in Southern Ontario in both pre-vaccine and vaccine eras, to estimate the underlying burden of pertussis in the population. The model was well calibrated using the best available data on pertussis in the pre-vaccination (1880–1929) and vaccination (1993–2004) eras in Ontario. Pertussis under-reporting by age group was estimated by comparing model-projected incidence to reported laboratory-confirmed cases for Greater Toronto. Best-fit model estimates gave a basic reproductive number of approximately 10.6, (seasonal range 9.9 to 11.5). Under-reporting increased with age, and approximately >95% of infections in children were caused by infections in persons with waning immunity to pertussis following prior infection or vaccination. A well-calibrated model suggests that under-recognized cases of pertussis in older individuals are likely to be an important driver of ongoing pertussis outbreaks in children. Model projections strongly support enhancement of booster vaccination efforts in adults.

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.

Pertussis Pseudo-outbreak linked to specimens contaminated by Bordetella pertussis DNA From clinic surfaces

BACKGROUND AND OBJECTIVES

We investigated a pertussis outbreak characterized by atypical cases, confirmed by polymerase chain reaction (PCR) alone at a single laboratory, which persisted despite high vaccine coverage and routine control measures. We aimed to determine whether Bordetella pertussis was the causative agent and advise on control interventions.

METHODS

We conducted case ascertainment, confirmatory testing for pertussis and other pathogens, and an assessment for possible sources of specimen contamination, including a survey of clinic practices, sampling clinics for B pertussis DNA, and review of laboratory quality indicators.

RESULTS

Between November 28, 2008, and September 4, 2009, 125 cases were reported, of which 92 (74%) were PCR positive. Cases occurring after April 2009 (n = 79; 63%) had fewer classic pertussis symptoms (63% vs 98%; P < .01), smaller amounts of B pertussis DNA (mean PCR cycle threshold value: 40.9 vs 33.1; P < .01), and a greater proportion of PCR-positive results (34% vs 6%; P < .01). Cultures and serology for B pertussis were negative. Other common respiratory pathogens were detected. We identified factors that likely resulted in specimen contamination at the point of collection: environmentally present B pertussis DNA in clinics from vaccine, clinic standard specimen collection practices, use of liquid transport medium, and lack of clinically relevant PCR cutoffs.

CONCLUSIONS

A summer pertussis pseudo-outbreak, multifactorial in cause, likely occurred. Recommendations beyond standard practice were made to providers on specimen collection and environmental cleaning, and to laboratories on standardizing PCR protocols and reporting results, to minimize false-positive results from contaminated clinical specimens.

Aerosolized vaccine as an unexpected source of false-positive Bordetella pertussis PCR results

When 13 of 13 nasal wash specimens from a single pediatrician's office tested positive for low quantities of Bordetella pertussis DNA, we suspected prelaboratory contamination. Investigation revealed that Pentacel and Adacel vaccines contain high copy numbers of B. pertussis DNA, which can be aerosolized, causing false-positive B. pertussis PCR results.

Novel multitarget real-time PCR assay for rapid detection of Bordetella species in clinical specimens

A novel multitarget real-time PCR (RT-PCR) assay for the rapid identification of Bordetella pertussis, B. parapertussis, and B. holmesii was developed using multicopy insertion sequences (ISs) in combination with the pertussis toxin subunit S1 (ptxS1) singleplex assay. The RT-PCR targets for the multiplex assay include IS481, commonly found in B. pertussis and B. holmesii; IS1001 of B. parapertussis; and the IS1001-like sequence of B. holmesii. Overall, 402 Bordetella species and 66 non-Bordetella species isolates were tested in the multitarget assay. Cross-reactivity was found only with 5 B. bronchiseptica isolates, which were positive with IS1001 of B. parapertussis. 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 all targets. A total of 197 human clinical specimens obtained during cough-illness outbreak investigations were used to evaluate the multitarget RT-PCR assay. The multiplex assay results from 87 clinical specimens were compared to the individual RT-PCR assay and culture results. The multitarget assay is useful as a diagnostic tool to confirm B. pertussis infections and to rapidly identify other Bordetella species. In conclusion, the use of this multitarget RT-PCR approach increases specificity, while it decreases the amount of time, reagents, and specimen necessary for RT-PCRs used for accurate diagnosis of pertussis-like illness.

Pertussis resurgence in Toronto, Canada: a population-based study including test-incidence feedback modeling

BACKGROUND

Pertussis continues to challenge medical professionals; recently described increases in incidence may be due to age-cohort effects, vaccine effectiveness, or changes in testing patterns. Toronto, Canada has recently experienced increases in pertussis incidence, and provides an ideal jurisdiction for evaluating pertussis epidemiology due to centralized testing. We evaluated pertussis trends in Toronto using all available specimen data, which allowed us to control for changing testing patterns and practices.

METHODS

Data included all pertussis culture and PCR test records for Greater Toronto from 1993 to 2007. We estimated incidence trends using Poisson regression models; complex relationships between disease incidence and test submission were explored with vector autoregressive models.

RESULTS

From 1993 to 2007, 26988 specimens were submitted for testing; 2545 (9.4%) were positive. Pertussis incidence was 2 per 100,000 from 1993 to 2004 and increased to 10 per 100,000 from 2005-2007, with a concomitant 6-fold surge in test specimen submissions after the introduction of a new, more sensitive PCR assay. The relative change in incidence was less marked after adjustment for testing volumes. Bidirectional feedbacks between test positivity and test submissions were identified.

CONCLUSIONS

Toronto's recent surge in pertussis reflects a true increase in local disease activity; the apparent size of the outbreak has likely been magnified by increasing use of pertussis testing by clinicians, and by improved test sensitivity since 2005. These findings may be applicable to changes in pertussis epidemiology that have been noted elsewhere in North America.

Recommendation for the use of newly introduced Tdap vaccine in Korea

Pertussis is an acute respiratory infection characterized by paroxysmal cough and inspiratory whoop for over 2 weeks. The incidence of pertussis has decreased markedly after the introduction of DTwP/DTaP vaccine, but the incidence of pertussis has increased steadily among young infant and among adolescents and adults in many countries. Td vaccine was used in this age group but the increase in pertussis has lead to the development of a Tdap vaccine. The Tdap vaccine is a Td vaccine with a pertussis vaccine added and is thought to decrease the incidence and transmission of pertussis in the respective age group. In Korea, two products are approved by the KOREA FOOD & DRUG ADMINISTRATION, which are ADACEL™ (Sanofi-Pasteur, Totonto, Ontario, Canada) and BOOSTRIX® (GlaxoSmithKline Biologicals, Rixensart, Belgium) for those aged between 11-64. This report summarizes the recommendations approved by the Committee on Infectious Diseases, the Korean Pediatric Society.

Real-time PCR-based detection of Bordetella pertussis and Bordetella parapertussis in an Irish paediatric population

Novel real-time PCR assays targeting the Bordetella pertussis insertion sequence IS481, the toxin promoter region and Bordetella parapertussis insertion sequence IS1001 were designed. PCR assays were capable of detecting ≤10 copies of target DNA per reaction, with an amplification efficiency of ≥90 %. From September 2003 to December 2009, per-nasal swabs and nasopharyngeal aspirates submitted for B. pertussis culture from patients ≤1 month to >15 years of age were examined by real-time PCR. Among 1324 patients, 76 (5.7 %) were B. pertussis culture positive and 145 (10.95 %) were B. pertussis PCR positive. Of the B. pertussis PCR-positive patients, 117 (81 %) were aged 6 months or less. A total of 1548 samples were examined, of which 87 (5.6 %) were culture positive for B. pertussis and 169 (10.92 %) were B. pertussis PCR positive. All culture-positive samples were PCR positive. Seven specimens (0.5 %) were B. parapertussis culture positive and 10 (0.8 %) were B. parapertussis PCR positive, with all culture-positive samples yielding PCR-positive results. A review of patient laboratory records showed that of the 1324 patients tested for pertussis 555 (42 %) had samples referred for respiratory syncytial virus (RSV) testing and 165 (30 %) were positive, as compared to 19.4 % of the total 5719 patients tested for RSV in this period. Analysis of the age distribution of RSV-positive patients identified that 129 (78 %) were aged 6 months or less, similar to the incidence observed for pertussis in that patient age group. In conclusion, the introduction of the real-time PCR assays for the routine detection of B. pertussis resulted in a 91 % increase in the detection of the organism as compared to microbiological culture. The incidence of infection with B. parapertussis is low while the incidence of RSV infection in infants suspected of having pertussis is high, with a similar age distribution to B. pertussis infection.

Pertussis in Florida, 2000-2006: trends in a historically low-incidence state

OBJECTIVE

Florida, the fourth most populous state in the nation, has had historically low incidence rates of pertussis, the only vaccine-preventable disease with increasing numbers of reported cases. We compared the epidemiology and incidence rates of pertussis in Florida with other states and the United States.

METHODS

We used Florida and federal surveillance data from 2000 through 2006.

RESULTS

Reported incidence of pertussis in Florida, numbers of cases, and proportions of adolescents and adults all increased during the seven-year study period. Florida incidence rates increased from 0.44 to 1.28, but the state's incidence was always ranked 45th or lower among the states. Reported pertussis cases and those among adolescents and adults in Florida increased during the study period. Ten counties, containing 60% of Florida's population, reported two-thirds of the state's cases.

CONCLUSIONS

Pertussis reported from Florida mirrored national trends with increasing incidence, numbers of cases, and proportions of adolescent and adult cases. Despite the increases, Florida maintained its historic pattern of pertussis incidence rates that are consistently lower than national figures. Limited laboratory diagnostics and a focus on the pediatric population likely contributed to the lower rates of pertussis in Florida. More emphasis on surveillance of adolescent and adult cases is needed.

Improved selective isolation of Bordetella pertussis by use of modified cyclodextrin solid medium

We have developed a modified cyclodextrin solid (MCS) medium using the selective antibiotic cefdinir. MCS medium exhibited higher sensitivity (95.6%; any culture-positive sample as reference) and greater inhibition of nasopharyngeal flora than did Bordet-Gengou agar (65.2%, P = 0.009) or cyclodextrin solid medium (39.1%, P < 0.001).

Outbreak of atypical pertussis detected by polymerase chain reaction in immunized preschool-aged children

BACKGROUND

From October 2005 to March 2006, a laboratory-confirmed outbreak of pertussis occurred in preschool-aged children (1-4 years) in Toronto, Canada. A case-control study in children was done to identify the risk factors for being positive for Bordetella pertussis by polymerase chain reaction (PCR).

METHODS

A case was defined as an individual 0 to 18 years of age who tested positive for B. pertussis by PCR in Toronto from October 2005 to March 2006. Each case was matched to 2 controls (negative for B. pertussis by PCR) by: (1) age, (2) geographic region of testing, and (3) date of testing.

RESULTS

One hundred eighty-nine cases and 296 controls were enrolled. Only 42% of cases (vs. 25% controls, P < 0.0001) met a clinical definition of pertussis, 3 cases (4 controls) were hospitalized, and the secondary household attack rate was 8%. One-third of cases were positive for another respiratory pathogen and >90% of cases and controls were up-to-date with pertussis immunization. Children attending school (matched odds ratio [ORm] = 5.2; 95% confidence intervals [CI]: 1.4-19.0), day care (ORm = 2.2; 95% CI: 1.2-4.0), visiting a doctor's office (ORm = 1.6; 95% CI: 1.0-2.5), or exposed to a household member (median age: 4-5 years) with a pertussis-like cough (ORm = 1.9; 95% CI: 1.0-3.6) were significantly more likely to have a positive PCR test for B. pertussis.

CONCLUSIONS

The main risk factors for PCR positivity for B. pertussis were school or day care attendance. Atypical symptoms were likely moderated by high immunization rates or may have been caused by other respiratory pathogens. In some cases, a positive PCR result might simply have reflected transient nasopharyngeal carriage of B. pertussis.

Epidemiology of pertussis and Haemophilus influenzae type b disease in Canada with exclusive use of a diphtheria-tetanus-acellular pertussis-inactivated poliovirus-Haemophilus influenzae type b pediatric combination vaccine and an adolescent-adult tetanus-diphtheria-acellular pertussis vaccine: implications for disease prevention in the United States

BACKGROUND

During the decade 1998-2007, a combination DTaP(5)-IPV/Hib vaccine was used exclusively in Canada to immunize infants and young children against diphtheria, tetanus, pertussis, polio, and invasive Haemophilus influenzae type b (Hib) disease.

METHODS

Medline was used to search for publications during 1996-2008 related to the epidemiology and vaccine prevention of pertussis and invasive Hib disease in Canada. Related abstracts and presentations were reviewed, when available, and epidemiologic data since 1985 were obtained from the Public Health Agency of Canada public Web site.

RESULTS

Reports of pertussis have declined substantially in preschool and school-aged children during the past decade, and cyclical peaks in disease incidence have been blunted or eliminated. In provinces and territories where Tdap(5) vaccine has been administered to 14- to 16-year-olds, marked reductions of pertussis have been documented in adolescents as well as younger age groups, possibly due to herd immunity. Incidence rates of invasive Hib disease among Canadian children <5 years declined markedly after introduction of Hib conjugate vaccines, and the disease has remained under control with exclusive use of DTaP(5)-IPV/Hib vaccine. Most cases of invasive Hib disease occur among unimmunized or only partially vaccinated children. The reduction of Hib case reports has been documented throughout Canada, including among Aboriginal children who are at high risk for this disease.

CONCLUSIONS

The Canadian experience with DTaP(5)-IPV/Hib and Tdap(5) vaccines is relevant to the United States because immunization schedules, vaccination coverage rates, and epidemiologic patterns of pertussis and Hib diseases are similar in the 2 countries, and because both vaccines are licensed for use in the United States.

[Bordetella pertussis in adolescent students in Mexico City]

OBJECTIVE

To estimate seroprevalence of Bordetella pertussis in students and their community.

METHODS

A total of 12,273 adolescent students aged 12 to 15 years from 14 public high schools in Mexico City were studied from September 2002 to March 2003. Nasopharyngeal samples were collected from those adolescents with whooping cough for more than 14 days. Infection was confirmed using polymerase chain reaction (PCR). All students, school staff and family exposed to PCR-confirmed cases were tested.

RESULTS

Whooping cough rate was 5 to 1,000 students. Of those students (61) who were identified with whooping cough for more than 14 days, 20 (32.8%) were positive to Bordetella pertussis. Of 152 people exposed (contacts) to these cases, 16 (10.6%) were positive and only eight (50%) had whooping cough. One of these exposed (contacts) was the principal of a school that had more than 60% positive cases (12/20) and who was also a teacher of 10 infected students. Of 29 family members tested, eight (27.6%) were positive and from three different families.

CONCLUSIONS

The study results show a similar rate of whooping cough in adolescents as seen in other countries. Since persistent cough is not always clinically seen in all infected individuals, there may be asymptomatic cases of Bordetella infection.

International Bordetella pertussis assay standardization and harmonization meeting report. Centers for Disease Control and Prevention, Atlanta, Georgia, United States, 19-20 July 2007

An international meeting on Bordetella pertussis assay standardization and harmonization was held at the Centers for Disease Control and Prevention (CDC), Atlanta, GA, 19–20 July 2007. The goal of the meeting was to harmonize the immunoassays used for pertussis diagnostics and vaccine evaluation, as agreed upon by academic and government researchers, regulatory authorities, vaccine manufacturers, and the World Health Organization (WHO).

The primary objectives were (1) to provide epidemiologic, laboratory, and statistical background for support of global harmonization; (2) to overview the current status of global epidemiology, pathogenesis and immunology of pertussis; (3) to develop a consensus opinion on existing gaps in understanding standardization of pertussis assays used for serodiagnosis and vaccine evaluation; and (4) to search for a multicenter process for addressing these priority gaps. Presentations and discussions by content experts addressed these objectives. A prioritized list of action items to improve standardization and harmonization of pertussis assays was identified during a group discussion at the end of the meeting. The major items included: (1) to identify a group that will organize, prepare, maintain, and distribute proficiency panels and key reagents such as reference and control sera; (2) to encourage the development and identification of one or more reference laboratories that can serve as an anchor and resource for other laboratories; (3) to define a performance-based assay method that can serve as a reference point for evaluating laboratory differences; (4) to develop guidance on quality of other reagents, e.g., pertussis toxin and other antigens, and methods to demonstrate their suitability; (5) to establish an international working group to harmonize the criteria to evaluate the results obtained on reference and proficiency panel sera; (6) to create an inventory to determine the amount of appropriate and well-characterized sera that are available globally to be used as bridging reagents for vaccine licensure; and (7) to seek specific guidance from regulatory authorities regarding the expectations and requirements for the licensure of new multicomponent pertussis vaccines.

Identification and evaluation of new target sequences for specific detection of Bordetella pertussis by real-time PCR

A comparative analysis of the Bordetella pertussis, B. bronchiseptica, and B. parapertussis genome assemblies permitted the identification of regions with significant sequence divergence and the design of two new real-time PCR assays, BP283 and BP485, for the specific detection of B. pertussis. The performance characteristics of these two assays were evaluated and compared to those of culture and an existing real-time PCR assay targeting the repetitive element IS481. The testing of 324 nasopharyngeal specimens indicated that, compared to culture, the BP283 assay had a sensitivity and specificity of 100 and 96.8% and the BP485 assay had a sensitivity and specificity of 92.3 and 97.1%. Notably, B. holmesii was isolated from two specimens that were positive by the IS481 assay but negative by the BP283 and BP485 assays. These two assays represent an improvement in specificity over those of PCR assays targeting only IS481 and may be duplexed or used in conjunction with existing PCR assays to improve the molecular detection of B. pertussis.

Pertussis: review of epidemiology, diagnosis, management and prevention

Bordetella pertussis--the cause of pertussis or whooping cough--is an exclusively human pathogen. Disease elimination by vaccination should, therefore, be possible, but has proved elusive. Many industrialised countries with long established immunisation programs are currently seeing a resurgence of pertussis, despite universal vaccination with high uptake, with the highest burden in the least immunised age groups (infants under 6 months of age and persons over 10 years old). However, low recognition and reporting and insensitive diagnostic tests mean that the true burden of pertussis is still underestimated. Recently, efforts to improve diagnostic yield include the expanded use of polymerase chain reaction and serological tests but both have significant limitations. The range of antibiotics available for treatment and prophylaxis has expanded to include the newer macrolides, azithromycin and clarithromycin, and a range of universal and targeted vaccination strategies have been implemented or proposed. This paper reviews the current epidemiology of pertussis in developed countries, including modes of clinical presentation, diagnosis, management and potential vaccination strategies.

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.

Pertussis vaccination for health care workers

Pertussis, an acute respiratory infection caused by Bordetella pertussis, classically manifests as a protracted cough illness. The incidence of pertussis in the United States has been increasing in recent years. Immunity wanes after childhood vaccination, leaving adolescents and adults susceptible to infection. The transmission of pertussis in health care settings has important medical and economic consequences. Acellular pertussis booster vaccines are now available for use and have been recommended for all adolescents and adults. These vaccines are safe, immunogenic, and effective. Health care workers are a priority group for vaccination because of their increased risk of acquiring infection and the potential to transmit pertussis to high-risk patients. Health care worker vaccination programs are likely to be cost-effective, but further research is needed to determine the acceptability of pertussis vaccines among health care workers, the duration of immunity after booster doses, and the impact of vaccination on the management of pertussis exposures in health care settings.

Implementation of a pertussis immunization program in a teaching hospital: an argument for federally mandated pertussis vaccination of health care workers

BACKGROUND

As pertussis disease becomes more common, health care-associated outbreaks have been reported with increasing frequency. Often, these clusters are costly and labor intensive to investigate and contain. It is clear that health care workers are among the adults who transmit pertussis to susceptible infants. Recent focus on patient safety, together with a concern for protecting employees in the workplace and those they expose elsewhere, has spurred interest in optimizing measures to prevent infection and disease transmission. Shortly after a tetanus toxoid, reduced diphtheria toxoid and acellular pertussis vaccine adsorbed booster was licensed and became available, we designed, launched, and analyzed a campaign to immunize the employees of our institution against pertussis.

METHODS

To optimize acceptance of a tetanus toxoid, reduced diphtheria toxoid and acellular pertussis vaccine adsorbed booster by employees, we adopted a program consisting of a 3-phase publicity and educational model and a 3-phase vaccine delivery approach.

RESULTS

Despite extraordinary resources dedicated to this program, and our institution's better than average annual uptake of influenza vaccine, less than one third of our eligible employees were immunized. A significant number of employees declined to be vaccinated for inappropriate reasons.

CONCLUSION

A campaign of this kind is quite labor intensive and expensive, yet limited overall vaccine uptake was achieved. A federal mandate to require pertussis immunization of all health care workers appears to be a more effective way to protect our patients, employees, families, and society.

Development and evaluation of dual-target real-time polymerase chain reaction assays to detect Bordetella spp

Novel, highly specific, and sensitive real-time polymerase chain reaction (PCR) assays using 2 targets, insertion sequence (IS481) and pertussis toxin subunit 1 (ptxS1), were developed to detect Bordetella pertussis and to differentiate between relevant Bordetella spp. Sixty-four non-Bordetella isolates were negative by both assays, demonstrating the specificity of the assays. B. pertussis, Bordetella parapertussis, and Bordetella holmesii isolates were specifically identified using the assays. The lower limit of detection was less than 10 genomic equivalents per reaction for the IS481 and ptxS1 assays. These assays were evaluated using 145 human clinical specimens obtained during cough-illness outbreak investigations, and PCR results were compared with Bordetella spp. culture results. Twenty-seven (18.6%) specimens had late positive cycle threshold (Ct) values (35 <or= Ct < 40) using the IS481 assay with corresponding negative results using the ptxS1 assay and culture and were considered indeterminate. Guidelines for use of PCR testing and interpretation of results during cough-illness outbreaks are discussed.

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.

Real-time polymerase chain reaction detection of Bordetella pertussis DNA in acellular pertussis vaccines

Using 2 real-time polymerase chain reaction (PCR) assays for Bordetella pertussis, 2 of 5 acellular pertussis vaccines were found to contain B. pertussis DNA. Because residual DNA in vaccines can cause environmental contamination, the administration of acellular pertussis vaccines to patients should be physically separated from the collection of patients' specimens for testing of B. pertussis DNA by real-time PCR.

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.

Outbreak of pertussis on a college campus

BACKGROUND

Pertussis is increasing among adolescents and adults despite universal childhood vaccination. This investigation describes an outbreak of pertussis among undergraduate students and assesses the burden of cough illness on a college campus.

METHODS

Students presenting with prolonged cough were evaluated with culture, polymerase chain reaction (PCR), and serology. An e-mail survey was performed to determine the burden of cough illness on campus.

RESULTS

Thirty-seven undergraduates were evaluated. Their mean duration of cough was 28 days. No student had cultures positive for B. pertussis; one was PCR positive. Ten (27%) had serologic values consistent with acute pertussis infection. The e-mail survey was returned by 225/500 (45%) students. Of these, 66 (29%; 95% confidence interval [CI], 23%-36%) reported a cough of 2 weeks or longer duration during the fall semester. A conservative estimate showed that the campus-wide incidence of a cough illness meeting the Centers for Disease Control and Prevention case definition for pertussis was 13% (95% CI, 10%-16%) during the fall semester.

CONCLUSIONS

Adolescents and young adults are susceptible to pertussis infection. This study demonstrates that there was a substantial rate of pertussis infection during an outbreak on a college campus. Our findings support the routine use of the acellular pertussis vaccine in adolescents and adults.

Multitarget PCR for diagnosis of pertussis and its clinical implications

PCR has greatly facilitated pertussis diagnosis due to the speed, sensitivity, and specificity of this assay compared to other detection methods. Various single-target PCR assays are currently utilized, but none is universally considered to be the "gold standard." Our aim was to assess the use of multitarget versus single-target PCR for the diagnosis of pertussis in clinical samples. PCR assays targeting insertion sequence IS481 (IS), pertussis toxin ptxA promoter region (PT), and outer membrane porin (PO), or recA (RA) were evaluated in respiratory specimens collected from 4,442 patients with suspected pertussis. The diagnosis of pertussis was confirmed in 309 (6.96%) patients by the 3-target IS-PT-PO/RA PCR versus 247 (5.56%) by the conventional single-target IS (P=0.007). Compared to single-target IS, the three-target combination increased the proportion of positive specimens by 1.25-fold, and two-target combinations increased the proportion of positive specimens by 1.10- to 1.24-fold. In addition, nine cases of B. parapertussis infection were also confirmed by using the discriminative features of this multitarget PCR. Of the 89 culture-proven pertussis cases, 17 (19.1%) and 5 of the 16 patients (31.3%) admitted to intensive care unit would have been missed had only the single-target IS PCR been applied. Patients with mild disease (P=0.004) and shorter hospitalization (P=0.006) were less likely to have positive cultures. This consensus generating real-time PCR approach permits a sensitive detection, as well as an accurate species identification of the causative Bordetella pathogens for the timely management of patients.

Rationale for use of Tdap booster vaccines for adolescent immunization: overview of efficacy, safety, and clinical use

Pertussis is one of the only vaccine-preventable diseases with increasing incidence in the United States. The incidence of pertussis infection in adolescents is a growing concern; it can be a severe disease that may lead to significant morbidity and mortality when transmitted to susceptible populations (eg, infants). Experts have conceded that booster vaccination of adolescents may considerably decrease the incidence of pertussis infections in previously immunized, partially immunized, and nonimmunized populations. Studies in 2 tetanus, diphtheria, and acellular pertussis (Tdap) booster vaccines licensed by the Food and Drug Administration (FDA) have shown efficacy against pertussis disease and have demonstrated a safety profile comparable to tetanus and diphtheria vaccine (Td) in adolescents. Immunization schedules now include use of Tdap vaccines for preadolescent and adolescent populations to counter the increase in pertussis outbreaks. Challenges for clinicians include prompt recognition of pertussis symptoms, proper diagnosis using appropriate tools, and timely reporting of pertussis infections to surveillance bodies. Additional studies are needed to monitor trends of pertussis incidence after implementing the new vaccination schedule for adolescents.

Recent developments in pertussis

Pertussis causes nearly 300,000 deaths in children every year. Most deaths take place in developing countries, but the infection remains a priority everywhere. Pertussis vaccination protects infants and children against death and admission to hospital, but breakthrough disease in vaccinated people can happen. In high-mortality countries, the challenge is to improve timeliness and coverage of childhood vaccination and surveillance. In regions with low mortality and highest coverage, pertussis is frequently the least well-controlled disease in childhood vaccination programmes. Some countries have reported a rise in pertussis in adolescents, adults, and pre-vaccination infants, but how much these changes are real or a result of improved recognition and surveillance remains uncertain. In response, several countries have introduced adolescent and adult acellular pertussis vaccine boosters. The effect so far is unknown; assessment is impeded by poor data. Uncertainties still persist about key variables needed to model and design vaccination programmes, such as risk of transmission from adults and adolescents to infants. New vaccination strategies under investigation include vaccination of neonates, family members, and pregnant women.

Outbreak of pertussis among healthcare workers in a hospital surgical unit

BACKGROUND

In September 1999, a pertussis outbreak was detected among surgical staff of a 138-bed community hospital. Patients were exposed to Bordetella pertussis during the 3-month outbreak period.

OBJECTIVE

To describe the outbreak among surgical staff, to evaluate implemented control measures, and to determine whether nosocomial transmission occurred.

METHODS

Clinical pertussis was defined as acute cough illness with a duration of 14 days or more without another apparent cause; persons with positive culture, PCR, or serologic test results were defined as having laboratory-confirmed pertussis. Surgical healthcare workers (HCWs) were interviewed regarding pertussis symptoms, and specimens were obtained for laboratory analysis. Patients exposed to B. pertussis during an ill staff member's 3-week infectious period were interviewed by phone to determine the extent of nosocomial spread.

PARTICIPANTS

A total of 53 HCWs assigned to the surgical unit and 146 exposed patients. HCWs with pertussis were defined as case subjects; HCWs without pertussis were defined as non-case subjects.

RESULTS

Twelve (23%) of 53 HCWs had clinical pertussis; 6 cases were laboratory confirmed. The median cough duration in the 12 case subjects was 27 days (range, 20-120 days); 10 (83%) had paroxysms. Eleven (92%) of 12 case subjects and 28 (86%) of 41 non-case subjects received antibiotic treatment or prophylaxis. Seven case subjects (58%) reported they always wore a mask when near patients. Of 146 patients potentially exposed to pertussis from the 12 case subjects, 120 (82%) were interviewed; none reported a pertussis-like illness.

CONCLUSIONS

Surgical staff transmitted B. pertussis among themselves; self-reported data suggests that these HCWs did not transmit B. pertussis to their patients, likely because of mask use, cough etiquette, and limited face-to-face contact. Control measures might have helped limit the outbreak once pertussis was recognized.

Pertussis in Infants, Children, and Adolescents: Diagnosis, Treatment, and Prevention

Pertussis, or "whooping cough," caused by the gram-negative pleomorphic bacillus Bordetella pertussis, is a highly contagious, potentially life-threatening respiratory tract illness that has re-emerged worldwide as a cause of substantial morbidity and mortality in infants, children, and adolescents, despite high vaccination rates. Increased awareness and reporting, in addition to the availability of better diagnostic tests, partially explain the recent resurgence of pertussis. However, waning immunity after childhood immunization has resulted in a growing pool of susceptible adolescents and adults who are capable of transmitting pertussis to vulnerable unvaccinated or incompletely vaccinated infants. An acellular pertussis vaccine booster for adolescents has been recommended in the United States and other industrialized countries. Active immunization and early diagnosis are crucial in the management of pertussis.