Diphtheria Outbreaks in Schools in Central Highland Districts, Vietnam, 2015–2018

Abstract

D iphtheria is a serious childhood disease with a high mortality rate (1). After a diphtheria-tetanus-pertussis vaccine (DTP) was introduced in the early 20th century, the number of cases dramatically decreased. Incidence reached a low of 4,333 cases in 2006, but more recently, the number of reported cases has increased, with incidence reaching 16,648 cases in 2018 (2). In 1981, Vietnam introduced a vaccination program in which participants received 3 primary doses of DTP (DTP3) vaccine; in 2011, a booster shot (DTP4) to be given 18 months after the initial doses was added (3). Although diphtheria cases had become sporadic by 2010, beginning in 2013, outbreaks occurred in the western and central highland areas of Vietnam, which prompted our study (4). The Study During June 2015-April 2018, the Pasteur Institute in Nha Trang, Vietnam, and the provincial health authority investigated 46 cases involving patients with suspected diphtheria, 8 of whom died, and 49 asymptomatic contacts in the provinces of Quang Nam and Quang Ngai in the central highlands region of Vietnam (Figure 1). We used standard case investigation forms to collect demographic and clinical information. We collected throat swab specimens from 93 patients and contacts but were unable to collect samples from 2 patients who had died. No cutaneous diphtheria was reported. We used sheep blood agar and tellurite medium cultures to identify Corynebacterium diphtheriae and extracted DNA with a QIAGEN DNA Mini Kit (QIA-GEN, https://www.qiagen.com), following a standard protocol. We used 2 sets of primers, Tox1/Tox2 and Dipht6F/Dipht6R, for PCR testing (5). The Elek test for diphtheria is not available in Vietnam. Laboratory testing confirmed diphtheria in 22 of 46 suspected cases: 17 patients, including 4 who died, tested positive in both culture and PCR tests, whereas 5 patients, including 1 who died, tested positive only

Endemic erythromycin resistant Corynebacterium diphtheriae in Vietnam in the 1990s

“…Our results outlined substantial genetic diversity among the Vietnamese C. diphtheriae population, with seven different STs identified. The most common STs (ST67) and the ST209 have also been identified in diphtheria outbreaks in the western and central highlands of Vietnam recently, implying the sustained circulation of these STs across the country [ 28 ]. ST67 was the most common genotype associated with diphtheria in an observational studies from San Lazaro Hospital in the Philippines and in Europe [ 49, 50 ], whereas ST258 and ST209 were both reported in Thailand in 2012 [ 51 ].…”

“…Here, using a historic collection of organisms and data we have investigated a collection of C. diphtheriae isolated in Vietnam in the 1990s, when erythromycin resistance was an emerging problem. Our data provide some additional context to C. diphtheriae in Vietnam and we can show that identical STs (67 and 209) have remained in circulation for >30 years and are capable of seeding new outbreaks [ 28 ]. Our results emphasize that historic collections of organisms improve the framework for ongoing surveillance for diseases that have not yet been eradicated and provide better context for the current trajectory in global antimicrobial resistance trends.…”

“…Diphtheria is endemic in Vietnam, although disease incidence declined rapidly after the introduction of the vaccine into the EPI in the late 1980s [25,26]. The incidence of diphtheria increased in Vietnam in the mid-1990s and there were several outbreaks, with some isolates exhibiting resistant to erythromycin [25,27,28]. There are little available data from this period, and no molecular characterisation of bacterial isolates from this period.…”

Non-toxigenic Corynebacterium diphtheriae in hallux ulceration

“…Although diphtheria was endemic in Cambodia in the 1980s, the latest report dates from 2010, with rare cases reported to the World Health Organization (WHO) between 2000 and 2010 [16]. However, several diphtheria cases have been described during the last decade in South-East Asia countries such as Thailand, Laos, Myanmar, Vietnam, Malaysia, and Indonesia, including a similar case of foot infection with a nontoxigenic C. diphtheriae biovar Gravis in a 16-year-old girl, who had traveled to Thailand [17][18][19][20][21][22][23]. The present finding of C. diphtheriae in Cambodia highlights the fact that this pathogen should be considered for microbiological analyses in a country where the laboratory capacities are limited and where antibiotics are freely dispensed by pharmacies without bacteriological documentation and medical prescription.…”

Seroepidemiology and Carriage of Diphtheria in Epidemic-Prone Area and Implications for Vaccination Policy, Vietnam

“…Because of efforts in vaccination, reported diphtheria cases in Vietnam decreased to nearly zero by 2010. However, several small diphtheria outbreaks in remote districts in central and western Vietnam have been observed since 2013 ( 7 ).…”