Macrolide-Resistant Bordetella pertussis, Vietnam, 2016-2017

Fatal Case of Macrolide-Resistant Bordetella pertussis Infection, Japan, 2024

Here, we present a fatal case of macrolide-resistant Bordetella pertussis (MRBP) infection in a 1-month-old female infant born prematurely at 34 weeks of gestation. The infant, unvaccinated against pertussis, exhibited respiratory failure, bilateral pneumonia, and hyperleukocytosis (109.8 × 109/L) on day 44 of life. Despite initial treatment with azithromycin and a high-flow nasal cannula, her condition deteriorated rapidly, requiring mechanical ventilation and venoarterial extracorporeal membrane oxygenation. The infant passed away four days after symptom onset. Nasopharyngeal swabs confirmed the presence of B. pertussis carrying an A2047G mutation in the 23S rRNA gene, resulting in significant macrolide resistance. Phylogenetic analysis indicated that the isolate was genetically closer to Chinese MT28-MRBP isolates than to previously identified Japanese isolates. The combination of early infancy and delayed administration of effective antimicrobials likely contributed to the unfavorable outcome in this case. It is imperative to monitor the global dissemination of MRBPs and enhance local diagnostic capabilities.

Pertussis in Early Infancy: Diagnostic Challenges, Disease Burden, and Public Health Implications Amidst the 2024 Resurgence, with Emphasis on Maternal Vaccination Strategies

Bordetella pertussis is the causative agent of pertussis or whooping cough, an acute and highly contagious respiratory infection that can have serious and fatal complications such as pneumonia, encephalopathy, and seizures, especially for newborns. The disease is endemic not only in the European Union (EU)/European Economic Area (EEA) but also globally. Larger outbreaks are anticipated every three to five years, even in countries where vaccination rates are high. Despite the high pertussis vaccination coverage in developed countries and a low rate of pertussis incidence for many years, especially during the COVID-19 pandemic, the incidence of pertussis has been on the rise again, with outbreaks in some places, which is referred to as "re-emergence of pertussis". The aim of this review is to underscore the critical importance of achieving high vaccination coverage, particularly among pregnant women, to safeguard vulnerable neonates from pertussis during their early months, before they are eligible for vaccination. This aligns with the need to address diagnostic challenges, mitigate disease severity, and strengthen public health strategies in light of the ongoing 2024 Bordetella pertussis resurgence.

Pertussis in the Post-COVID-19 Era: Resurgence, Diagnosis, and Management

Pertussis is endemic worldwide, with epidemics occurring every 2 to 5 years despite a high vaccination coverage. After limited circulation during the coronavirus disease 2019 (COVID-19) pandemic, pertussis cases have increased rapidly worldwide since mid-late 2023, returning to pre-pandemic patterns. In Korea, 90 cases of pertussis were reported from April 2020 to May 2023, with elderly individuals aged ≥65 years accounting for 48.9%. Pertussis cases have increased sharply since June 2024, showing a nationwide epidemic, with a large increase among adolescents aged 13-15 years. As of August 2024, the national incidence rate of pertussis was estimated to be 37.75 per 100,000 population, with the highest incidence of 526.2 per 100,000 population in 13-year-olds. In Europe, during 2023-2024, an increase in pertussis incidence among infants was observed, along with large increases in 10-19-year-olds. In China, the number of reported cases of pertussis has increased rapidly since late 2023, with an age shift to older children, increase of vaccine escape, and a marked increase in the prevalence of macrolide-resistant Bordetella pertussis. The recent global resurgence of pertussis is due to decreased opportunities for boosting immunity by natural infection during the COVID-19 pandemic in combination with waning of immunity-induced pertussis vaccines.

Lonidamine, a Novel Modulator for the BvgAS System of Bordetella Species

The Gram-negative bacteria Bordetella pertussis, B. parapertussis, and B. bronchiseptica cause respiratory diseases in various mammals. They share the BvgAS two-component system, which regulates the phenotypic conversion between the virulent Bvg+ and avirulent Bvg- phases. In the BvgAS system, the sensor kinase BvgS senses environmental cues and transduces a phosphorelay signal to the response regulator BvgA, which leads to the expression of Bvg+ phase-specific genes, including virulence factor genes. Bacteria grown at 37°C exhibit the Bvg+ phenotype. In contrast, at lower than 26°C or in the presence of modulators, such as MgSO4 and nicotinic acid, the BvgAS system is inactivated, leading bacteria to the avirulent Bvg- phase. Therefore, effective modulators are expected to provide a therapeutic measure for Bordetella infection; however, no such modulators are currently available, and the mechanism by which modulators inactivate the BvgAS system is poorly understood. In the present study, we identified lonidamine as a novel modulator after screening an FDA-approved drug library using bacterial reporter systems with the Bvg+-specific and Bvg--specific promoters. Lonidamine directly bound to the VFT2 domain of BvgS and inactivated the BvgAS system at concentrations as low as 50 nM, which was at least 2000- to 20,000-fold lower than the effective concentrations of known modulators. Lonidamine significantly reduced the adherence of B. pertussis to cultured cells but unexpectedly exacerbated bacterial colonization of the mouse nasal septum. These results provide insights into the structural requirements for BvgAS modulators and the role of Bvg phenotypes in the establishment of infection.

Phenotypic diversity of Bordetella pertussis against Trimethoprim/Sulphamethoxazole in vitro tests

BACKGROUND

Trimethoprim/sulfamethoxazole (TMP/SMZ), traditionally a second-line drug, is now proposed as the primary alternative treatment for macrolide-resistant Bordetella pertussis (B.pertussis). Thus, there is an urgent need to evaluate the phenotypic profile of B. pertussis regarding susceptibility to TMP/SMZ.

METHODS

Kirby-Bauer (KB) disk diffusion methods and E-test strips were employed to assess the in vitro susceptibility profiles of 128 B. pertussis strains isolated in China between 2017 and 2022 against TMP/SMZ. Additionally, whole genome sequencing was performed on one strain exhibiting a heterogeneous phenotype.

RESULTS

B. pertussis displayed three phenotypes to TMP/SMZ based on the first 10 days of culture: a predominant fuzzy-bordered phenotype (118/128, 92.2 %), a minority with a clear-bordered phenotype (8/128, 6.3 %), and a sporadic heterogeneous phenotype (2/128, 1.6 %) where TMP/SMZ heterozygous colonies emerged on the 9th day of incubation. The diameter of the inhibition zone around the paper disk will decrease as the culture time extends, while the MIC value will change in the opposite direction. Almost in all tests, the bacterial colony will cover the entire inhibitory zone after 10-14 days of incubation. Strains exhibiting heterogeneity were compared with the complete genomes of Tohama I and CS strains, and 191 and 179 point mutation sites were identified, respectively, with multiple variants associated with the expression of transcriptional regulators.

CONCLUSION

This study highlights the diverse drug sensitivity phenotypes of B. pertussis to TMP/SMZ and the importance of uniform testing protocols. Continuous and dynamic monitoring of B. pertussis isolates for TMP/SMZ sensitivity, along with investigating its correlation with epidemiological changes, is essential for establishing a scientific foundation for the effective management and control of pertussis.

Severe pertussis in infants: a scoping review

BACKGROUND

Pertussis (Whooping Cough) is a respiratory infection caused by Bordetella pertussis. Pertussis usually occurs in childhood; severe infections are most common in infants. It can be fatal with severe complications such as pulmonary hypertension, heart failure, and encephalitis.

OBJECTIVES

We sought to synthesize the existing literature on severe pertussis in infants and inform further study.

METHODS

A scoping review was performed based on the methodological framework developed by Arksey & O'Malley. Search in Pubmed and Embase databases, with no restrictions on the language and date of publication.

RESULTS

Of the 1299 articles retrieved, 64 were finally included. The selected articles were published between 1979 and 2022, with 90.6% (58/64) of the studies in the last two decades. The studies covered epidemiology, pathology, clinical characteristics, risk factors, treatments, and burden of disease.

CONCLUSION

The literature reviewed suggests that studies on severe pertussis in infants covered a variety of clinical concerns. However, these studies were observational, and experimental studies are needed to provide high-quality evidence.

Severe problem of macrolides resistance to common pathogens in China

With the widespread use of macrolide antibiotics in China, common pathogens causing children's infections, such as Streptococcus pneumoniae, Streptococcus (including Group A streptococcus, Group B streptococcus), Staphylococcus aureus, Bordetella pertussis, and Mycoplasma pneumoniae, have shown varying degrees of drug resistance. In order to provide such problem and related evidence for rational use of antibiotics in clinic, we reviewed the drug resistance of common bacteria to macrolides in children recent 20 years.

The whole-cell proteome shows the characteristics of macrolides-resistant Bordetella pertussis in China linked to the biofilm formation

The macrolides-resistant Bordetella pertussis (MR-Bp) isolates in China evolved from the ptxP1/fhaB3 allele and rapidly became predominant, suggestive of an adaptive transmission ability. This was different from the global prevalent ptxP3 strains, in which MR-Bp was rarely reported. The study aimed to determine the underlying mechanism responsible for fitness and resistance in these two strains. We identify proteomic differences between ptxP1/fhaB3 and ptxP3/fhaB1 strains using tandem mass tag (TMT)-based proteomics. We then performed in-depth bioinformatic analysis to determine differentially expressed genes (DEGs), followed by gene ontology (GO), and protein-protein interaction (PPI) network analysis. Further parallel reaction monitoring (PRM) analysis confirmed the expression of four target proteins. Finally, the crystal violet method was used to determine biofilm-forming ability. The results showed that the main significantly different proteins between the two represent isolates were related to biofilm formation. Furthermore, we have confirmed that ptxP1/fhaB3 showed hyperbiofilm formation in comparison with ptxP3/fhaB1. It is suggested that the resistance and adaptability of ptxP1/fhaB3 strains may be related to the formation of biofilm through proteomics. In a word, we determined the significantly different proteins between the ptxP1/fhaB3 and ptxP3/fhaB1 strains through whole-cell proteome, which were related to biofilm formation.

Young Zambian infants with symptomatic RSV and pertussis infections are frequently prescribed inappropriate antibiotics: a retrospective analysis

Pediatric community-acquired pneumonia (CAP) remains a pressing global health concern, particularly in low-resource settings where diagnosis and treatment rely on empiric, symptoms-based guidelines such as the WHO's Integrated Management of Childhood Illness (IMCI). This study details the delivery of IMCI-based health care to 1,320 young infants and their mothers in a low-resource urban community in Lusaka, Zambia during 2015. Our Southern Africa Mother Infant Pertussis Study (SAMIPS) prospectively monitored a cohort of mother/infant pairs across infants' first four months of life, recording symptoms of respiratory infection and antibiotics prescriptions (predominantly penicillins), and tested nasopharyngeal (NP) samples for respiratory syncytial virus (RSV) and Bordetella pertussis. Our retrospective analysis of the SAMIPS cohort found that symptoms and antibiotics use were more common in infants (43% and 15.7%) than in mothers (16.6% and 8%), while RSV and B. pertussis were observed at similar rates in infants (2.7% and 32.5%) and mothers (2% and 35.5%), albeit frequently at very low levels. In infants, we observed strong associations between symptoms, pathogen detection, and antibiotics use. Critically, we demonstrate that non-macrolide antibiotics were commonly prescribed for pertussis infections, some of which persisted across many weeks. We speculate that improved diagnostic specificity and/or clinician education paired with timely, appropriate treatment of pertussis could substantially reduce the burden of this disease while reducing the off-target use of penicillins.

Genotyping and macrolide-resistant mutation of Bordetella pertussis in East and South-East Asia

OBJECTIVES

Macrolide-resistant Bordetella pertussis (MRBP) has been emerging and prevailing in mainland China since 2011. In this study, we aimed to investigate the genotype and macrolide resistance of circulating B. pertussis in East and Southeast Asia using genetic analyses.

METHODS

A total of 302 DNA extracts from clinical specimens and isolates from 2010 to 2020 were analyzed: 145 from Vietnam, 76 from Cambodia, 48 from Taiwan, and 33 from Japan. Genotypes were determined by multilocus variable-number tandem-repeat analysis (MLVA). Macrolide-resistant A2047G mutation in B. pertussis 23S rRNA was investigated using the duplex Cycleave real-time polymerase chain reaction (PCR) assay. Whole-genome sequencing was performed on two MRBP isolates that were identified for the first time in Taiwan.

RESULTS

Overall, 286 DNA extracts (95%) generated a complete MLVA genotype and 283 DNA extracts (94%) yielded a complete result for the A2047G mutation analysis. The A2047G mutation was detected in 18 DNA extracts: fourteen from Vietnam, one from Cambodia, two from Taiwan, and one from Japan. Most of them (78%) showed the genotypes MT104 and MT195, which have previously been reported in Chinese MRBP isolates. Further, the Taiwanese MRBP isolates were classified into the MT104 clade of Chinese MRBP isolates.

CONCLUSION

After MRBP emerged and spread in mainland China, it may have spread to East and Southeast Asia in the 2010s. Continued surveillance targeting the A2047G mutation of MRBP is needed to prevent further spread of this emerging pathogen.

Macrolide Resistance in Bordetella pertussis: Current Situation and Future Challenges

Pertussis is a highly contagious respiratory infection caused by Bordetella pertussis bacterium. The mainstay of treatment is macrolide antibiotics that reduce transmissibility, shorten the duration of symptoms and decrease mortality in infants. Recently, the macrolide resistance of B. pertussis has been reported globally but is especially widespread in mainland China. In this review, we aim to summarise the current understanding of the epidemiology, resistance mechanisms and clinical implications of B. pertussis macrolide resistance. Since the first appearance of macrolide-resistant B. pertussis in Arizona, USA, in 1994, only sporadic cases have been reported outside China. In certain parts of China, on the other hand, up to 70-100% of the recent clinical isolates have been found to be macrolide resistant. Reasons for macrolide resistance being centred upon China during the last decade can only be speculated on, but the dominant B. pertussis lineage is different between China and most of the high-income countries. It seems evident that efforts to increase awareness, guide molecular epidemiological surveillance and carry out systematic screening of B. pertussis positive samples for macrolide resistance should be implemented globally. In addition, practices to improve the clinical care of infants with pertussis caused by resistant strains should be studied vigorously.

Complete Genome Sequence of a Macrolide-Resistant Bordetella pertussis Isolated in Japan

We report the complete genome sequence of macrolide-resistant Bordetella pertussis BP616, which was first isolated in 2018 in Japan. The BP616 genome can serve as a valuable specific reference for genomic and epidemiological studies of this resistant bacterium.

Genomic and transcriptomic variation in Bordetella spp. following induction of erythromycin resistance

Background

The emergence of macrolide resistance in Bordetella pertussis, the causative agent of pertussis, due to mutations in the 23S rRNA gene has been recently recognized. However, resistance mechanisms to macrolides in Bordetella parapertussis and Bordetella holmesii remain unknown.

Objectives

This study investigated genomic changes induced by in vitro exposure to erythromycin in these three main pathogens responsible for pertussis-like disease.

Methods

A set of 10 clinical and reference strains of B. pertussis, B. parapertussis and B. holmesii was exposed to erythromycin for 15 weeks or 30 subculture passages. Antibiotic pressure was achieved by growth on the selective media with erythromycin Etest strips or impregnated discs. Genome polymorphisms and transcriptomic profiles were examined by short- and long-read sequencing of passaged isolates.

Results

B. parapertussis and B. holmesii isolates developed significant in vitro resistance to erythromycin (MIC >256 mg/L) within 2 to 7 weeks and at 5 to 12 weeks, respectively. B. pertussis remained phenotypically susceptible to the antibiotic following 15 weeks of exposure, with the MIC between 0.032 to 0.38 mg/L. Genomic analysis revealed that B. holmesii developed resistance due to mutations in the 23S rRNA gene. The resistance mechanism in B. parapertussis was hypothesized as being due to upregulation of an efflux pump mechanism.

Conclusions

These findings indicate that both B. holmesii and B. parapertussis can be more prone to induced resistance following exposure to treatment with erythromycin than B. pertussis. The surveillance of macrolide resistance in Bordetella isolates recovered from patients with pertussis, especially persistent disease, is warranted.

A Cross-Sectional Study Revealing the Emergence of Erythromycin-Resistant Bordetella pertussis Carrying ptxP3 Alleles in China

Background

Previous limited studies have identified that Bordetella pertussis (B. pertussis) isolates circulating in China possess distinct molecular features and high rates of erythromycin-resistance (ER). Their evolution and potential impact on the prevention and control of global pertussis are worthy of attention.

Methods

The present cross-sectional study involved 311 non-duplicate and unrelated B. pertussis strains isolated from Chinese children from 2017 to 2019. Their antimicrobial susceptibilities were assessed using both E-test strips and Kirby-Bauer (KB) disk diffusion methods. Seven virulence-related genes (ptxA, ptxC, ptxP, prn, fim2, fim3, and tcfA2) and the A2047G mutation in the 23S rRNA gene were detected by PCR. Based on the susceptibilities and genotypes, 50 isolates were selected for multi-locus variable-number tandem-repeat analysis (MLVA) typing and whole-genome sequencing.

Results

A total of 311 B. pertussis strains were isolated from children with a median age of 4 months (interquartile range: 2–9 months). Strains carrying the ptxP1 allele were more frequent (84.9%, 264/311), were always ER (except for one strain), and were mainly related to ptxA1/ptxC1/prn1 alleles (99.6%, 263/264). The remaining 47 (15.1%) strains carried the ptxP3 allele, mainly harboring the ptxA1/ptxC2/prn2 alleles (93.6%, 44/47), and were sensitive to erythromycin (except for two strains). The two ER-ptxP3 isolates were first identified in China, belonged to MT27 and MT28 according to MLVA, and were classified into sub-lineage IVd by phylogenetic analysis of their genome sequences. This sub-lineage also includes many strains carrying the ptxP3 allele spreading in developed countries. For each tested antimicrobial, the susceptibilities judged by KB disks were consistent with those determined by E-test strips.

Conclusion

The present results reveal that B. pertussis strains with the ptxP1-ER profile still dominate in China, and a few strains carrying the ptxP3 allele have acquired the A2047G mutation in the 23S rRNA gene and the ER phenotype. The surveillance of the drug susceptibility of B. pertussis is necessary for all countries, and the KB disk method can be adopted as a screening test.

Association Between Real-time Polymerase Chain Reaction Cycle Threshold Value and Clinical Severity in Neonates and Infants Infected With Bordetella pertussis

BACKGROUND

Polymerase chain reaction (PCR) is highly sensitive and is thus the standard method for diagnosing pertussis. Real-time PCR is widely used because of its accuracy and the simplicity of the simultaneous cycle threshold (Ct) value, which represents the copy numbers of the target gene. Little is known of the association of Ct value with pertussis severity in neonates and infants.

METHODS

This study determined Ct values in neonates and infants diagnosed with pertussis by real-time PCR using nasopharyngeal samples at Vietnam National Children's Hospital in Hanoi in 2017 and 2019. The association of disease severity and clinical parameters were analyzed using univariate and multivariate analyses.

RESULTS

We evaluated 108 patients with pertussis [median age: 63 days, interquartile range (IQR): 41-92 days]. Only 6/108 (6%) received at least 1 dose of a pertussis-containing vaccine. Among them, 24 (22.2%) had severe disease requiring care in a pediatric intensive care unit, 16 (13.8%) required mechanical ventilation, and 3 (2.6%) died. The median Ct value was lower in patients with severe disease (19.0, IQR: 16.5-22.0, n = 24) than in those without severe disease (25.5, IQR: 20.0-30.0, n = 84) (P = 0.002). Logistic regression analyses demonstrated that PCR Ct value [odds ratio (OR): 1.783, 95% confidence interval (CI): 1.013-3.138, P = 0.045], age (OR: 3.118, 95% CI: 1.643-5.920, P = 0.001), and white blood cell counts (OR: 0.446, 95% CI: 0.261-0.763, P = 0.003) remained significantly associated with severe disease.

CONCLUSIONS

Real-time PCR Ct values for pertussis might be useful as a predictor of severe disease in neonates and infants.

The First Reported Case of Bordetella pertussis Bacteremia in a Patient With Human Immunodeficiency Virus Infection

We describe a case of bacteremia in a human immunodeficiency virus–infected patient caused by a Bordetella pertussis strain lacking 2 major virulence factors, filamentous hemagglutinin and fimbriae. Although B pertussis bacteremia is uncommon, physicians should be aware that even attenuated B pertussis strains can cause invasive infection in immunocompromised patients.

Bordetella pertussis is a gram-negative coccobacillus that causes a severe paroxysmal coughing disease known as whooping cough or pertussis. Bordetella pertussis colonizes the epithelial cells of the human respiratory tract, and the organisms are typically isolated from nasopharynx. We describe a case of B pertussis bacteremia in a patient with human immunodeficiency virus (HIV) infection. Interestingly, the isolate recovered from blood culture did not produce the major virulence factors, filamentous hemagglutinin (FHA) and fimbriae (FIM). Previously, 3 cases of B pertussis bacteremia were reported in the literature. We discuss the features of B pertussis bacteremia.

JMM Profile: Bordetella pertussis and whooping cough (pertussis): still a significant cause of infant morbidity and mortality, but vaccine-preventable

Whooping cough (pertussis) is a highly contagious respiratory bacterial infection caused by Bordetella pertussis and is an important cause of morbidity and mortality worldwide, particularly in infants. Bordetella parapertussis can cause a similar, but usually less severe pertussis-like disease. Bordetella pertussis has a number of virulence factors including adhesins and toxins which allow the organism to bind to ciliated epithelial cells in the upper respiratory tract and interfere with host clearance mechanisms. Typical symptoms of pertussis include paroxysmal cough with characteristic whoop and vomiting. Severe complications and deaths occur mostly in infants. Laboratory confirmation can be performed by isolation, detection of genomic DNA or specific antibodies. Childhood vaccination is safe, effective and remains the best control method available. Many countries have replaced whole-cell pertussis vaccines (wP) with acellular pertussis vaccines (aP). Waning protection following immunisation with aP is considered to be more rapid than that from wP. Deployed by resource-rich countries to date, maternal immunisation programmes have also demonstrated high efficacy in preventing hospitalisation and death in infants by passive immunisation through transplacental transfer of maternal antibodies.

Intranasal Vaccine Delivery Technology for Respiratory Tract Disease Application with a Special Emphasis on Pneumococcal Disease

This mini-review will cover recent trends in intranasal (IN) vaccine delivery as it relates to applications for respiratory tract diseases. The logic and rationale for IN vaccine delivery will be compared to methods and applications accompanying this particular administration route. In addition, we will focus extended discussion on the potential role of IN vaccination in the context of respiratory tract diseases, with a special emphasis on pneumococcal disease. Here, elements of this disease, including its prevalence and impact upon the elderly population, will be viewed from the standpoint of improving health outcomes through vaccine design and delivery technology and how IN administration can play a role in such efforts.

Retrospective analysis of bacterial culture-confirmed pertussis cases in Beijing Children's hospital from 2014 to 2019 reveals prevention and control of the grim situation in mainland China

BACKGROUND

Our study aims to explore the epidemiological features of children with bacterial culture-confirmed pertussis visiting Beijing Children's Hospital, China.

METHODS

From 2014 through 2019, patients with suspected pertussis coming from mainland China provided nasopharyngeal swabs and bacterial culture that was subsequently cultivated.

RESULTS

During the study period, 6956 children with suspected pertussis from 30 different administrative provinces of mainland China were investigated, of which 1494 cases (21.5%) had positive B. pertussis culture. The number of pertussis cases increased year-on-year, from 122 in 2014 to 279 in 2019. Of the confirmed cases, 38.2% and 26.8% were identified in the summer and autumn, respectively. The age distribution of children with pertussis showed that 77.2% were <12 months old, including 56.0% <6 months old. Only thirteen B. parapertussis isolates and one B. bronchiseptica isolates were collected in the present samples.

CONCLUSIONS

The present culture-confirmed cases reveal the severe epidemic situation of pertussis spreading over the whole country and mainly affecting the infants. It is necessary to set up hospital-based surveillance with reliable laboratory methods to promote clinical awareness and to monitor the disease.

Pharmacotherapy for Bordetella pertussis infection. I. A synthesis of laboratory sciences

There is considerable history and practice experience both with laboratory susceptibility testing for Bordetella pertussis and clinical treatment. This two-part narrative review provides a synthesis of the laboratory and clinical sciences as they apply to this bacterium and the clinical consequences of treating infection. It is generally held that antibiotic susceptibility testing for B. pertussis is not sufficiently standardised, but there has not been an urgent need to consolidate the same given the lack global experience with major resistance profiles. Experience in China, however, has provided concern for high-level macrolide resistance. The nature of and frequency of such resistance has raised the bar for reconsideration of susceptibility testing given that first-line treatment may be regionally compromised. Disk diffusion and Etest susceptibility testing can be recommended for screening resistance among individual isolates of B. pertussis and on an ad hoc manner. Disk diffusion, Etest and/or critical agar dilution testing can be recommended for large-scale studies. Standards for inoculum, growth atmosphere, timing of interpretation, preferred testing media and controls can be extrapolated from the publications to date. Such methods should be able to detect high-level resistance to several antibiotics, but especially macrolides. Concern for intermediate-susceptible categories requires consideration as well as the correlation with bacteriological and clinical outcomes. Provisional standards can be applied at this time, and modification or fine-tuning of any such standards are open to future investigation.