Pertussis in Lao PDR: Seroprevalence and disease

Objectives Pertussis is a debilitating vaccine-preventable infection. The aim of this study was to determine susceptibility and exposure to pertussis in Lao PDR in different age groups and subpopulations. Methods A total 3072 serum samples were obtained from different cohorts: children with documented vaccination, pre-schoolers, schoolchildren, blood donors, healthcare workers (HCWs), and pregnant women and paired cord blood. Samples were tested for anti-pertussis toxin IgG antibodies. A history of Bordetella pertussis exposure was defined according to antibody titres. Four hundred and seventy-five throat swabs and nasopharyngeal aspirates were analysed by PCR for the presence of B. pertussis in symptomatic children at the Children's Hospital in Vientiane. Results Overall pertussis seroprevalence was 57.5%. The prevalence of titres indicating acute infection or recent vaccination or infection/vaccination within the last 12 months ranged from 7.4% (100/1356) in adults to 21.4% (25/117) in pre-schoolers (age 1–5 years). B. pertussis was detected in 1.05% (5/475) of children with respiratory symptoms in Vientiane Capital. Conclusions It is suggested that routine childhood vaccination, in particular outreach, as well as vaccination of HCWs should be strengthened. A childhood booster and vaccination of pregnant mothers should be considered. There is also a need to improve reporting and to introduce pertussis testing in at least one central facility

Evaluation of nationwide supplementary immunization in Lao People's Democratic Republic: Population-based seroprevalence survey of anti-measles and anti-rubella IgG in children and adults, mathematical modelling and a stability testing of the vaccine.

BACKGROUND: Measles outbreaks have occurred in some countries despite supplementary immunization activities (SIA) using measles-containing vaccine with high vaccination coverage. We conducted a cross-sectional seroprevalence survey to estimate population immunity in Lao People's Democratic Republic where repeated mass immunization has failed to eliminate measles. METHODS AND FINDINGS: In this nationwide multistage cluster sampling survey conducted in 2014 based on probability proportionate to size sampling, blood samples were collected from 2,135 children and adults living in 52 randomly selected villages. Anti-measles and anti-rubella IgG were measured, and IgG prevalence was calculated. We applied mathematical modelling to estimate the number of cases of congenital rubella syndrome (CRS) in 2013 that were averted by the 2011 SIA. A stability testing was applied to the MR vaccine at 4°C, 25°C, and 35°C to examine stability differences between measles and rubella vaccine components. Measles IgG prevalence was significantly lower in the target age groups (5-21 years) of the 2011 SIA using a combination vaccine for measles and rubella vaccine (MR vaccine) than in young adults (22-39 years) (86.8% [95% CI: 83.0-90.6] vs. 99.0% [98.3-99.8]; p<0.001), whereas rubella IgG prevalence was significantly higher (88.2% [84.5-91.8] vs. 74.6% [70.7-78.5]; p<0.001). In the SIA target age groups, prevalence of measles IgG, but not rubella IgG, increased with age. CRS cases prevented in 2013 ranged from 16 [0-50] to 92 [32-180] if the force of infection had remained unchanged or had been reduced by 75%, respectively. In freeze-dried conditions, the measles vaccine component was more heat sensitive than the rubella component. CONCLUSIONS: Inconsistent IgG prevalence between measles and rubella in Lao PDR can be partly explained by different stability of the measles and rubella vaccine components under heat exposure. Suboptimal vaccine handling may cause insufficient immunogenicity for measles, which subsequently leads to an outbreak despite high SIA coverage, while direct evidence is lacking. Temperature monitoring of the vaccine should be conducted

Emergence of chikungunya in Moonlapamok and Khong Districts, Champassak Province, the Lao People’s Democratic Republic, May to September 2012

Introduction: Chikungunya is a vector-borne disease transmitted to humans by Aedes mosquitoes, which are widespread in the Lao People’s Democratic Republic. However, chikungunya virus (CHIKV) had not been detected in the country before outbreaks reported in July 2012. The first outbreaks were detected through health care worker event-based surveillance. Methods: The case definition for the outbreaks was defined as a person with acute onset of fever (> 38 °C) and severe arthralgia (joint pain) or arthritis from 1 May 2012 in Champassak Province. Rapid response teams conducted active case finding, performed an environmental assessment including an entomological survey and implemented control measures. Descriptive analysis was undertaken in Microsoft Excel. Results: There were 197 cases (attack rate 3.4%) of suspected chikungunya reported from 10 villages in Moonlapamok and Khong Districts of Champassak Province. All age groups (age range: seven months–74 years) were affected with slightly more female (56%) than male cases. Thirty-one per cent (16 of 52) of serum samples tested positive for CHIKV by polymerase chain reaction. The environmental assessment found poor water storage practices and high entomological indices. Discussion: These outbreaks show the effectiveness of health care worker event-based surveillance and the importance of sharing of information across borders for detecting emerging diseases. Public health education is an important measure to prevent epidemics of chikungunya. Information about chikungunya should be supplied to health care workers in the region so they are alert to the potential spread and are able to implement control measures for this disease

Seroprevalence of chronic hepatitis B, as determined from dried blood spots, among children and their mothers in central Lao People's Democratic Republic: a multistage, stratified cluster sampling survey

Background: There is limited information regarding the prevalence of hepatitis B in Lao PDR, where the hepatitis disease burden is substantial. Thus, reliable seroprevalence data is needed for the disease, based on probability sampling. Methods: A stratified, multistage, cluster sampling survey of hepatitis B surface antigen (HBsAg) positivity among children aged 5–9 years and their mothers aged 15–45 years was conducted. Participants were selected randomly from the central region of Lao PDR via probability-proportional-to-size sampling. Blood samples were collected onto filter paper and subsequently analyzed using a chemiluminescent microparticle immunoassay. Results: A total of 911 mother-and-child pairs were collected; the seroprevalence of HBsAg was estimated to be 2.1% (95% confidence interval 0.8–3.4%) among children and 4.1% (95% confidence interval 2.6–5.5%) in their mothers after taking into account the sampling design and the weight of each sample. The children's HBsAg positivity was positively associated with maternal infection and being born in a non-health facility, while the maternal infection status was not associated with any background characteristic. Conclusions: Lao PDR has a relatively lower HBsAg prevalence in the general population compared to surrounding countries. To ensure comparability to other countries and to future data, rapid field tests are recommended for a nationwide prevalence survey

Stability testing of reconstituted measles and rubella combination vaccines.

<p>After incubation of reconstituted vaccines at 4°C (A), 25°C (B), or 35°C (C), titres of measles and rubella viruses in the vaccines were measured by plaque assays. Filled squares and open circles indicate titres of measles and rubella viruses, respectively. Means of three vials are shown. Error bars indicate standard deviations.</p

Best-fitting values of the force of infection in Lao PDR before the 2011 SIA among participants aged < 15 and ≥ 15 years, obtained by the selected best-fitting model (model B) for different assumptions about the reduction in the force of infection after the SIA, and CRS incidence per 100,000 live births among women aged 15–44 years after weighting by the number of live births occurring among women in different maternal age groups.

<p>Best-fitting values of the force of infection in Lao PDR before the 2011 SIA among participants aged < 15 and ≥ 15 years, obtained by the selected best-fitting model (model B) for different assumptions about the reduction in the force of infection after the SIA, and CRS incidence per 100,000 live births among women aged 15–44 years after weighting by the number of live births occurring among women in different maternal age groups.</p

Comparison between the predictions of age-specific percentage seronegative, obtained using the best-fitting catalytic model and the observed data.

<p>Bars reflect 95% confidence intervals of the observed data. Lines reflect predictions from the best-fitting model.</p

Reported coverage of routine immunization and supplementary immunization activities with measles containing vaccine by age at the survey in Lao PDR, 2014^*.

<p>Reported coverage of routine immunization and supplementary immunization activities with measles containing vaccine by age at the survey in Lao PDR, 2014^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0194931#t001fn001" target="_blank">*</a>}.</p

Rubella IgG seroprevalence measured by ELISA in different age groups from representative populations in Lao PDR, 2014.

<p>*An ELISA value of 10 IU/ml was considered positive. †Individuals 5 to 14 years old and 15 to 21 years old were among the targeted age groups of supplementary immunization activities conducted in 2011 using the MR combination vaccine with coverage of 97%. Their IgG prevalence was estimated to be 88.2% (95%CI: 84.5–91.8).</p

Stability testing of freeze-dried measles and rubella combination vaccines.

<p>After incubation of freeze-dried vaccines at 4°C (A), 25°C (B), or 35°C (C), titres of measles and rubella viruses in the vaccines were measured by plaque assays. Filled squares and open circles indicate titres of measles and rubella viruses, respectively. Means of three vials are shown. Error bars indicate standard deviations.</p