Diphtheria in Latvia, 1986-1996

Whole Genome Sequencing for Surveillance of Diphtheria in Low Incidence Settings

Corynebacterium diphtheriae (C. diphtheriae) is a relatively rare pathogen in most Western countries. While toxin producing strains can cause pharyngeal diphtheria with potentially fatal outcomes, the more common presentation is wound infections. The diphtheria toxin is encoded on a prophage and can also be carried by Corynebacterium ulcerans and Corynebacterium pseudotuberculosis. Currently, across Europe, infections are mainly diagnosed in travelers and refugees from regions where diphtheria is more endemic, patients from urban areas with poor hygiene, and intravenous drug users. About half of the cases are non-toxin producing isolates. Rapid identification of the bacterial pathogen and toxin production is a critical element of patient and outbreak management. Beside the immediate clinical management of the patient, public health agencies should be informed of toxigenic C. diphtheriae diagnoses as soon as possible. The collection of case-related epidemiological data from the patient is often challenging due to language barriers and social circumstances. However, information on patient contacts, vaccine status and travel/refugee route, where appropriate, is critical, and should be documented. In addition, isolates should be characterized using high resolution typing, in order to identify transmissions and outbreaks. In recent years, whole genome sequencing (WGS) has become the gold standard of high-resolution typing methods, allowing detailed investigations of pathogen transmissions. De-centralized sequencing strategies with redundancy in sequencing capacities, followed by data exchange may be a valuable future option, especially since WGS becomes more available and portable. In this context, the sharing of sequence data, using public available platforms, is essential. A close interaction between microbiology laboratories, treating physicians, refugee centers, social workers, and public health officials is a key element in successful management of suspected outbreaks. Analyzing bacterial isolates at reference centers may further help to provide more specialized microbiological techniques and to standardize information, but this is also more time consuming during an outbreak. Centralized communication strategies between public health agencies and laboratories helps considerably in establishing and coordinating effective surveillance and infection control. We review the current literature on high-resolution typing of C. diphtheriae and share our own experience with the coordination of a Swiss-German outbreak.

More than 20 years after re-emerging in the 1990s, diphtheria remains a public health problem in Latvia

In 1994, the World Health Organization (WHO) declared the goal of eliminating diphtheria within the WHO European Region by the year 2000. However, in 1990 an epidemic emerged within the Russian Federation and spread to other countries, including Latvia, by 1994. We describe national surveillance and immunisation coverage data in Latvia from 1994 to 2014 and present historical data from 1946. We defined a laboratory-confirmed case as a clinical case in which toxin-producing Corynebacterium diphtheriae, C. ulcerans or C. pseudotuberculosis was isolated. From 1994 to 2014, 1,515 cases were reported, giving an average annual incidence of 3.2 cases per 100,000 inhabitants (range 0.1–14.8), with the highest incidence in age groups 5–19 and 40–49 years (4.4 and 4.3/100,000, respectively); 111 deaths were reported, 83.8% cases were laboratory-confirmed. Most cases occurred in unvaccinated adults. To improve disease control a supplementary immunisation campaign for adults was initiated in 1995, and by the end of 1998 national coverage among adults reached 70%, and reached 77% in 2003, but declined to 59% by 2014. Diphtheria remains a problem in Latvia with continued circulation of toxin-producing strains of C. diphtheriae. We recommend to strengthen immunisation to cover adults, as well as the education of health professionals and a serological survey.

Seroepidemiology of diphtheria and tetanus among children and young adults in Tajikistan: nationwide population-based survey, 2010

BACKGROUND

Tajikistan had a major diphtheria outbreak (≈ 10,000 cases) in the 1990 s, which was controlled after nationwide immunization campaigns with diphtheria-tetanus toxoid in 1995 and 1996. Since 2000, only 52 diphtheria cases have been reported. However, in coverage surveys conducted in 2000 and 2005, diphtheria-tetanus-pertussis vaccine coverage was lower than administratively reported estimates raising concerns about potential immunity gaps. To further assess population immunity to diphtheria in Tajikistan, diphtheria antibody testing was included in a large-scale nationwide serosurvey for vaccine-preventable diseases conducted in connection with a poliomyelitis outbreak in 2010. In addition, the serosurvey provided an opportunity to assess population immunity to tetanus.

METHODS

Residents of all regions of Tajikistan aged 1-24 years were included in the serosurvey implemented during September-October 2010. Participants were selected through stratified cluster sampling. Specimens were tested for diphtheria antibodies using a Vero cell neutralization assay and for tetanus antibodies using an anti-tetanus IgG ELISA. Antibody concentrations ≥ 0.1 IU/mL were considered seropositive.

RESULTS

Overall, 51.4% (95% CI, 47.1%-55.6%) of participants were seropositive for diphtheria and 78.9% (95% CI, 74.7%-82.5%) were seropositive for tetanus. The lowest percentages of seropositivity for both diseases were observed among persons aged 10-19 years: diphtheria seropositivity was 37.1% (95% CI, 31.0%-43.7%) among 10-14 year-olds, and 35.3% (95% CI, 29.9%-41.1%) among 15-19 year-olds; tetanus seropositivity in respective age groups was 65.3% (95% CI, 58.4%-71.6%) and 70.1% (95% CI, 64.5%-75.2%).

CONCLUSIONS

Population immunity for diphtheria in Tajikistan is low, particularly among 10-19 year-olds. Population immunity to tetanus is generally higher than for diphtheria, but is suboptimal among 10-19 year-olds. These findings highlight the need to improve routine immunization service delivery, and support a one-time supplementary immunization campaign with diphtheria-tetanus toxoid among birth cohorts aged 1-19 years in 2010 (3-21 years in 2012) to close immunity gaps and prevent diphtheria outbreaks.

Respiratory diphtheria among highly vaccinated military trainees in Latvia: improved protection from DT compared with Td booster vaccination

An outbreak of respiratory diphtheria occurred among highly-vaccinated trainees at a Latvian military academy in August-September 2000. We reviewed immunization, clinical and laboratory records and administered a questionnaire to obtain data on exposure factors. Among 207 trainees, 45 (22%) diphtheria cases and 79 (38%) carriers of toxigenic Corynebacterium diphtheriae were identified. All patients survived; 1 had severe myocarditis. Sharing cups was a risk factor for infection. Over 85% of trainees had received > or =5 doses of diphtheria toxoid. Neither infection nor disease was associated with the number of doses or interval since last dose. However, the risk of disease was lower and diphtheria antitoxin levels were higher among trainees who received their last booster dose with higher-antigen diphtheria toxoid (DT) instead of lower-antigen Td. Outbreaks of mild diphtheria can occur among highly-vaccinated persons living in crowded conditions with intense exposure; high-antigen diphtheria booster-vaccination might provide better protection under these conditions.

Diphtheria with polyneuropathy in a closed community despite receiving recent booster vaccination

INTRODUCTION AND METHODS

We report 20 patients aged 18-24 years from Latvia with diphtheritic polyneuropathy. All lived in a closed community and 80% were known to have been fully vaccinated against diphtheria until at least 14 years old. Diphtheria antitoxin had been administered within 3 days of the onset of upper respiratory tract infection in 16 patients and 15 received antibiotics.

RESULTS

Neurological symptoms developed after a median of 43 days (range 35-58) compared to only 10 days in previous studies of unvaccinated patients. All showed evidence of mild limb polyneuropathy with electrophysiological evidence of polyneuropathy. Only 30% showed early bulbar abnormalities compared to the usual rate of over 95% in diphtheritic polyneuropathy. However, 45% had later bulbar deterioration coinciding with the limb polyneuropathy.

CONCLUSIONS

These patients show that an attenuated form of polyneuropathy of later onset, with less prominent early bulbar features, can occur in patients vaccinated against diphtheria according to schedule but living in a closed community in a country where diphtheria remains endemic.

Successful control of epidemic diphtheria in the states of the Former Union of Soviet Socialist Republics: lessons learned

Epidemic diphtheria reemerged in the Russian Federation in 1990 and spread to all Newly Independent States (NIS) and Baltic States by the end of 1994. Factors contributing to the epidemic included increased susceptibility of both children and adults, socioeconomic instability, population movement, deteriorating health infrastructure, initial shortages of vaccine, and delays in implementing control measures. In 1995, aggressive control strategies were implemented, and since then, all affected countries have reported decreases of diphtheria; however, continued efforts by national health authorities and international assistance are still needed. The legacy of this epidemic includes a reexamination of the global diphtheria control strategy, new laboratory techniques for diphtheria diagnosis and analysis, and a model for future public health emergencies in the successful collaboration of multiple international partners. The reemergence of diphtheria warns of an immediate threat of other epidemics in the NIS and Baltic States and a longer-term potential for the reemergence of vaccine-preventable diseases elsewhere. Continued investment in improved vaccines, control strategies, training, and laboratory techniques is needed.