Summary Infections frequently contain multiple strains (genotypes) of the same pathogen, yet they are still usually treated as uniform entities. In this Review, we discuss problems with inconsistent definition of the term "strain" and review the prevalence and implications of multiple-strain infections. Up to now, multiple-strain infections have been shown unambiguously in 51 human pathogens (and 21 non-human ones) and are likely to arise in most pathogen species. In human pathogens, multiple-strain infections usually reach considerable frequencies (median 11·3%, mean 21·7% of infections), which are certainly underestimated in many cases because of technical limitations of detection. For many diseases, the importance of multiple-strain infections is still unclear, but theoretical work and experimental results from animal models suggest a broad range of clinically relevant effects. Multiple-strain infections can affect host immune responses and our ability to prevent and treat infection efficiently. Competition and mutualism between strains change pathogen and disease dynamics and promote pathogen evolution. Co-infection enables gene transfer among strains. Taking multiple-strain infections into account will improve our understanding of host-pathogen interactions and disease dynamics, and will provide a basis for novel control approaches.

https://www.thelancet.com/pdfs/journals/laninf/PIIS1473-3099(11)70241-9.pdf

Prevalence and implications of multiple-strain infections

Background. Traveler’s diarrhea in Thailand is frequently caused by Campylobacter jejuni. Rates of fluoroquinolone (FQ) resistance in Campylobacter organisms have exceeded 85% in recent years, and reduced fluoroquinolone efficacy has been observed. Methods. Azithromycin regimens were evaluated in a randomized, double-blind trial of azithromycin, given as a single 1-g dose or a 3-day regimen (500 mg daily), versus a 3-day regimen of levofloxacin (500 mg daily) in military field clinics in Thailand. Outcomes included clinical end points (time to the last unformed stool [TLUS] and cure rates) and microbiological end points (pathogen eradication). Results. A total of 156 patients with acute diarrhea were enrolled in the trial. Campylobacter organisms predominated (in 64% of patients), with levofloxacin resistance noted in 50% of Campylobacter organisms and with no azithromycin resistance noted. The cure rate at 72 h after treatment initiation was highest (96%) with single-dose azithromycin, compared with the cure rates of 85% noted with 3-day azithromycin and 71% noted with levofloxacin ( ). Single-dose azithromycin was also associated with the shortest median TLUS (35 h; P p .002 , by log-rank test). Levofloxacin’s efficacy was inferior to azithromycin’s efficacy, except in patients with P p .03 no pathogen identified during the first 24 h of treatment or in patients with levofloxacin-susceptible Campylobacter isolates, in whom it appeared to be equal to azithromycin. The rate of microbiological eradication was significantly better with azithromycin-based regimens (96%–100%), compared with levofloxacin (38%) ( ); however, P p .001 this finding was poorly correlated with clinical outcome. A higher rate of posttreatment nausea in the 30 min after receipt of the first dose (14% vs. !6%; ) was observed as a mild, self-limited complaint associated P p .06 with single-dose azithromycin. Conclusions. Single-dose azithromycin is recommended for empirical therapy of traveler’s diarrhea acquired in Thailand and is a reasonable first-line option for empirical management in general.

/pdf/traveler-s-diarrhea-in-thailand-randomized-double-blind-2imgxkjk1h.pdf

Traveler's diarrhea in Thailand: randomized, double-blind trial comparing single-dose and 3-day azithromycin-based regimens with a 3-day levofloxacin regimen.

Objectives: To review Campylobacter cases in England and Wales over 2 decades and examine the main factors/mechanisms driving the changing epidemiology. Design: A descriptive study of Campylobacter patients between 1989 and 2011. Cases over 3 years were linked anonymously to postcode, population density, deprivation indices and census data. Cases over 5 years were anonymously linked to local weather exposure estimates. Setting: Patients were from general practice, hospital and environmental health investigations through primary diagnostic laboratories across England and Wales.

https://bmjopen.bmj.com/content/bmjopen/2/4/e001179.full.pdf

Campylobacter epidemiology: a descriptive study reviewing 1 million cases in England and Wales between 1989 and 2011

A rapid duplex real-time polymerase chain reaction (PCR) assay for speciation of Campylobacter jejuni and Campylobacter coli using the ABI Prism 7700 sequence detection system (Applied Biosystems) was developed based on two of the genes used in a conventional multiplex PCR A rapid turnaround time of 3 h was achieved with the use of boiled cell lysates Applicability of the assay was tested with 6015 random campylobacter strains referred to the Campylobacter Reference Unit, with 976% being identified as either C jejuni or C coli by this technique Rapidity, combined with specificity and sensitivity, makes this method for routine campylobacter speciation attractive to any laboratory with a Taqman system

Applicability of a rapid duplex real-time PCR assay for speciation of Campylobacter jejuni and Campylobacter coli directly from culture plates

The Campylobacter excretion patterns of 26 domestic pet dogs were described in a longitudinal study. The dogs entered the study between 3 and 8 months of age and were monitored until 2 years of age. They were tested monthly for Campylobacter carriage in stool samples that were cultured on the Campylobacter-selective media CAT and modified CCDA agar at 37 and 42°C. This study comprised 366 fecal swab samples, of which 278 (76.2%) were found to be Campylobacter positive, with the following distribution of species: 75.0% Campylobacter upsaliensis, 19.4% Campylobacter jejuni, 2.1% Campylobacter lari, 0.7% Campylobacter coli, and 2.8% Campylobacter spp. Isolates were typed by pulsed-field gel electrophoresis (PFGE) to elucidate the strain excretion pattern. All study dogs excreted Campylobacter spp. during the study period. At 3 months of age, 60% of the dogs carried Campylobacter, increasing to nearly 100% carriers at 1 year of age, whereafter the carriage rate decreased to 67% at 24 months of age. The PFGE types showed that individual dogs were often colonized by unique strains of C. upsaliensis for several months, up to 21 months or longer. These C. upsaliensis strains were either clonal (or underwent concurrent minor mutative changes) or independent strains. In contrast, the excreted C. jejuni isolates were much more diverse and, in most cases, only seen in one sample from each dog. A high degree of diversity among different dogs was seen. We conclude that young domestic pet dogs excreted Campylobacter spp. during the majority of their puppyhood and adolescent period. In general C. upsaliensis strains were excreted for months, with short-term interruptions by or cocolonization with other transitory Campylobacter spp., predominantly C. jejuni. C. jejuni was more prevalent in dogs between 3 months and 1 year of age than in dogs between 1 and 2 years of age.

Longitudinal Study of the Excretion Patterns of Thermophilic Campylobacter spp. in Young Pet Dogs in Denmark

Aims: To determine the frequency of coinfection with multiple strains in sporadic cases of human Campylobacter infection.



Method and Results: During 1999 10 single colonies of Campylobacter were cultured from each of 53 positive faecal samples. Five isolates were taken from nonselective agar after passive filtration of faecal suspensions and five isolates were taken from selective agar plates. All isolates were sero- and phage typed and their antibiotic resistance determined. Pulsed-field gel electrophoresis and flagellin gene typing were performed on selected isolates. One patient was infected with Camp. coli, the remainder with strains of Camp. jejuni. The majority of patients was infected with a single strain of Campylobacter, but from each of four samples, 7·5%, two strains of Camp. jejuni, confirmed by molecular typing, were identified.



Conclusions: Coinfection occurs in sporadic cases of campylobacteriosis.



Significance and Impact of the Study: This study has implications in outbreak investigation when distinct strains have been isolated from epidemiologically related patients and/or the suspected source or vehicle.

D.R.A. Wareing

Papers

Coinfection with Campylobacter species: an epidemiological problem?