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
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D iphtheria is an infectious disease caused by toxigenic strains of Corynebacterium diphtheriae, C. ulcerans, and, rarely, C. pseudotuberculosis (1-3). Although the diphtheria toxoid vaccine contributed to a decrease in the number of diphtheria cases globally, the disease remains a threat to public health, particularly in South and Southeast Asia (4,5).Currently, the World Health Organization recommends 3 primary doses of the diphtheria-tetanuspertussis (DTP) vaccine in young infants (i.e., at 6, 10, and 14 weeks of age), followed by 3 booster doses at 12-23 months, 4-7 years, and 9-15 years of age, to protect all age groups. Nevertheless, many low-and middle-income countries have not introduced all booster doses.The Vietnamese Ministry of Health (MOH) first introduced DTP in 1981, targeting infants 2, 3, and 4 months of age. A booster dose targeting children 18 months of age was introduced during 2011 (6). 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).Supplemental immunization activities (SIAs), in which vaccination is delivered to all targeted persons regardless of their previous vaccination history, were conducted in the areas surrounding Quang Ngai Province when diphtheria cases were identified during 2013-2019 (8). However, most of the population of Quang Ngai Province has not been covered by SIAs as of October 2019. According to the national surveillance program, Quang Ngai Province reported 2 laboratory-confirmed cases in 2017-2018 and 47 in 2019-2020, among an estimated population of 1,231,697 (9). Among these cases, 36 (73%) cases were in school-age children (6-17 years of age). Among confirmed cases, 3 (6%) were fatal.Although national administrative coverage of 3 doses of DTP among infants has been maintained
Background Infants are at highest risk of pneumococcal disease. Their added protection through herd effects is a key part in the considerations on optimal pneumococcal vaccination strategies. Yet, little is currently known about the main transmission pathways to this vulnerable age group. Hence, this study investigates pneumococcal transmission routes to infants in the coastal city of Nha Trang, Vietnam. Methods and findings In October 2018, we conducted a nested cross-sectional contact and pneumococcal carriage survey in randomly selected 4- to 11-month-old infants across all 27 communes of Nha Trang. Bayesian logistic regression models were used to estimate age specific carriage prevalence in the population, a proxy for the probability that a contact of a given age could lead to pneumococcal exposure for the infant. We used another Bayesian logistic regression model to estimate the correlation between infant carriage and the probability that at least one of their reported contacts carried pneumococci, controlling for age and locality. In total, 1,583 infants between 4 and 13 months old participated, with 7,428 contacts reported. Few infants (5%, or 86 infants) attended day care, and carriage prevalence was 22% (353 infants). Most infants (61%, or 966 infants) had less than a 25% probability to have had close contact with a pneumococcal carrier on the surveyed day. Pneumococcal infection risk and contact behaviour were highly correlated: If adjusted for age and locality, the odds of an infant’s carriage increased by 22% (95% confidence interval (CI): 15 to 29) per 10 percentage points increase in the probability to have had close contact with at least 1 pneumococcal carrier. Moreover, 2- to 6-year-old children contributed 51% (95% CI: 39 to 63) to the total direct pneumococcal exposure risks to infants in this setting. The main limitation of this study is that exposure risk was assessed indirectly by the age-dependent propensity for carriage of a contact and not by assessing carriage of such contacts directly. Conclusions In this study, we observed that cross-sectional contact and infection studies could help identify pneumococcal transmission routes and that preschool-age children may be the largest reservoir for pneumococcal transmission to infants in Nha Trang, Vietnam.
Background: Infants are at highest risk of pneumococcal disease. Their added protection through herd effects is a key part in the considerations on optimal pneumococcal vaccination strategies. Yet, little is currently known about the main transmission pathways to this vulnerable age group. Methods and findings: We conducted a nested cross-sectional contact and nasopharyngeal swabbing survey in randomly selected infants across all 27 communes of Nha Trang, Vietnam. Bayesian logistic regression models were used to estimate age specific carriage prevalence in the population, a proxy for the probability that a contact of a given age could lead to pneumococcal exposure for the infant. We used another Bayesian logistic regression model to estimate the correlation between infant carriage and the probability that at least one of their reported contacts carried pneumococci, controlling for age and locality. In total 1583 infants between 4 and 13 months old participated, with 7428 contacts reported. Few infants (5%) attended day care and carriage prevalence was 22%. Most infants (61%) had less than a 25% probability to have had close contact with a pneumococcal carrier on the surveyed day. Pneumococcal infection risk and contact behaviour were highly correlated: if adjusted for age and locality the odds of an infant's carriage increased by 22% (95%CI:15-29) per 10 percentage points increase in the probability to have had close contact with at least one pneumococcal carrier. Two to six year old children contributed 51% (95%CI: 39-63) to the total pneumococcal exposure risks to infants in this setting. Conclusions: Cross-sectional contact and infection studies can help identify pneumococcal transmission routes. In Nha Trang, preschool age children are the largest reservoir for pneumococcal transmission to infants.
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