Pneumococcal colonization and severity of pneumonia in hospitalized Cambodian children following introduction of the 13-valent pneumococcal conjugate vaccine.

Objectives: This study sought to characterize pneumococcal colonization and clinical/radiological features in Cambodian children admitted to hospital with an illness compatible with pneumonia following national introduction of the 13-valent pneumococcal conjugate vaccine (PCV13). Methods: Children aged 0-59 months admitted to Angkor Hospital for Children who met the World Health Organization (WHO) case definition for clinical pneumonia were enrolled over a 3-year period. Clinical, radiological and vaccination data were collected at enrolment. A nasopharyngeal swab was collected for detection of pneumococcal colonization using the WHO standard culture method. Results: Between 1 September 2015 and 31August 2018, 2209 analysable illness episodes were enrolled. Pneumococci were detected in 943/2209 (42.7%) children. PCV13 serotypes were detected less frequently in children who had been vaccinated appropriately for their age compared with undervaccinated children: 309/567 (53.6%) vs 216/342 (63.2%) (P=0.006). Age-appropriate PCV13 vaccination was negatively associated with hypoxic presentation [adjusted odds ratio (aOR) 0.72, 95% confidence interval (CI) 0.60-0.87; P=0.0006] and primary endpoint pneumonia on chest x ray (aOR 0.69, 95% CI 0.54-0.90; P=0.006). Conclusions: The introduction of PCV13 in Cambodia was associated with a decline in vaccine serotype nasopharyngeal colonization, and clinical and radiological severity in children hospitalized with clinical pneumonia.

Residual risk of mother-to-child transmission of HBV despite timely Hepatitis B vaccination: a major challenge to eliminate hepatitis B infection in Cambodia.

BACKGROUND: In countries with intermediate or high hepatitis B virus (HBV) endemicity, mother-to-child transmission (MTCT) represents the main route of chronic HBV infection. There is a paucity of information on HBV MTCT in Cambodia. This study aimed to investigate the prevalence of HBV infection among pregnant women and its MTCT rate in Siem Reap, Cambodia. METHODS: This longitudinal study included two parts, study-1 to screen HBsAg among pregnant women and study-2 to follow up babies of all HBsAg-positive and one-fourth of HBsAg-negative mothers at their delivery and six-month post-partum. Serum or dried blood spot (DBS) samples were collected to examine HBV sero-markers by chemiluminescent enzyme immunoassay (CLEIA), and molecular analyses were performed on HBsAg-positive samples. Structured questionnaires and medical records were used to examine the risk factors for HBV infection. MTCT rate was calculated by HBsAg positivity of 6-month-old babies born to HBsAg-positive mothers and ascertained by the homology of HBV genomes in mother-child pair at 6-month-old. RESULTS: A total of 1,565 pregnant women were screened, and HBsAg prevalence was 4.28% (67/1565). HBeAg positivity was 41.8% and was significantly associated with high viral load (p < 0.0001). Excluding subjects who dropped out due to restrictions during COVID-19, one out of 35 babies born to HBsAg-positive mothers tested positive for HBsAg at 6 months of age, despite receiving timely HepB birth dose and HBIG, followed by 3 doses of HepB vaccine. Hence the MTCT rate was 2.86%. The mother of the infected baby was positive for HBeAg and had a high HBV viral load (1.2 × 109 copies/mL). HBV genome analysis showed 100% homology between the mother and the child. CONCLUSIONS: Our findings illustrate the intermediate endemicity of HBV infection among pregnant women in Siem Reap, Cambodia. Despite full HepB vaccination, a residual risk of HBV MTCT was observed. This finding supports the recently updated guidelines for the prevention of HBV MTCT in 2021, which integrated screening and antiviral prophylaxis for pregnant women at risk of HBV MTCT. Furthermore, we strongly recommend the urgent implementation of these guidelines nationwide to effectively combat HBV in Cambodia.

Prevalence of total hepatitis A antibody among 5 to 7 years old children and their mothers in Cambodia.

This study determined the prevalence of total hepatitis A antibody (anti-HAV) among 5-7 years old children and their mothers in the whole Cambodia, using a nationwide study, and examined the differences between the two cohorts. A total of 4535 dried blood spot-driven (DBS) samples (2021 mothers and their 2514 children of 5-7 years old) and the concomitant 922 whole blood samples (subset of the whole participants) were collected using a multistage random sampling strategy throughout Cambodia in 2017. Total anti-HAV was detected using the chemiluminescence enzyme immunoassay method. Compared to gold standard whole blood samples, the sensitivity and specificity of DBS mediated anti-HAV detection were 94.8% and 98%, respectively. Total anti-HAV prevalence among mothers was 91.2% (95%CI: 90.0-92.5%), and that of their children was 31.5% (95%CI: 29.7-33.3%). In our study, the low prevalence of total anti-HAV among children indicates the country's improvement of safe water and food supply, hygiene and sanitation. If the hygiene and sanitation are consistently improved in Cambodia, the prevalence might be no longer increased when the children become adults.

Existence of hepatitis B virus surface protein mutations and other variants: demand for hepatitis B infection control in Cambodia.

BACKGROUND: This study aimed to detect Hepatitis B virus (HBV) genome sequences and their variants as of nationwide scale using dried blood spot (DBS) samples and to provide up-to-date reference data for infection control and surveillance in Cambodia. METHOD: Among 2518 children age 5-7 years and their 2023 mothers participated in 2017 Cambodia nationwide sero-survey on hepatitis B surface antigen (HBsAg) prevalence using multistage random sampling strategy, 95 mothers and 13 children positive to HBsAg were included in this study. HBV DNA was extracted from DBS, then performed polymerase chain reaction. HBV genotypes and potential variants were examined by partial and full length genomic analysis. RESULTS: HBsAg positive rate was 4.7% (95/2023) in mothers and 0.52% (13/2518) in their children. Genotype C (80.49%) was abundantly found throughout the whole Cambodia whilst genotype B (19.51%) was exclusively found in regions bordering Vietnam. S gene mutants of HBV were found in 24.29% of mothers and 16.67% of children with HBV DNA positive sera. Full-length genome analysis revealed the homology of 99.62-100% in each mother-child pair. Genotype B was clarified to recombinant genotype B4/C2 and B2/C2. Double (48.39%) and combination mutation (32.26%) were observed in core promoter region of HBV C1 strains. CONCLUSIONS: This study showed the capable of DBS for large-scale molecular epidemiological study of HBV in resource limited countries. Full-genome sequences yield the better understanding of sub-genotypes, their variants and the degree of homology between strains isolated from mother-child pairs calls for effective strategies on prevention, control and surveillance of mother-to-child HBV transmission in Cambodia.

Evaluation of the efficiency of dried blood spot-based measurement of hepatitis B and hepatitis C virus seromarkers.

Although hepatitis B (HBV) and C (HCV) virus infections are still global health issues, measuring sero-markers by standard venipuncture is challenging in areas limited with the adequate human resources and basic infrastructure. This study aimed to inform the usefulness of dried blood spot (DBS) sampling technique for epidemiological study of HBV and HCV in the resources limited areas. We compared specimen recovery rate expressed as analytical sensitivity ratio of HBsAg, HBcAb and anti-HCV between serum specimens and DBS samples (HemaSpot vs Whatman903). Sensitivity ratio was calculated as the ratio of the measured value from DBS to the measured value from serum. Then both the qualitative and quantitative comparisons of HBsAg detection by DBS were done using Cambodian samples. HBsAg, HBcAb and anti-HCV sensitivity ratios for the highest sample dilution (8-fold) were 31.2:1, 38.9:1 and 32.0:1 for Whatman903 card and 17.6:1, 23.5:1 and 26.3:1 for HemaSpot respectively. Detection efficacy of HemaSpot (80%) was not inferior to Whatman903 (60%) after 1 month storage, and no significant difference in any hepatitis virus sero-markers was observed in HemaSpot-spotted patient samples stored for 2 weeks at -25 °C and 29 °C. All reference HemaSpot -spotted 400 HBsAg sero-negative samples showed negative. Sensitivity and specificity of HBsAg in HemaSpot were 92.3% and 100%. The recovery expressed as analytical sensitivity ratio of HBsAg, HBcAb and anti-HCV of HemaSpot specimen were not inferior to Whatman903. Therefore, DBS with its usefulness proved as an acceptable tool for large epidemiological study of HBV and HCV in resources limited remote area.

Impact of 13-Valent Pneumococcal Conjugate Vaccine on Colonization and Invasive Disease in Cambodian Children.

BACKGROUND: Cambodia introduced the 13-valent pneumococcal conjugate vaccine (PCV13) in January 2015 using a 3 + 0 dosing schedule and no catch-up campaign. We investigated the effects of this introduction on pneumococcal colonization and invasive disease in children aged <5 years. METHODS: There were 6 colonization surveys done between January 2014 and January 2018 in children attending the outpatient department of a nongovernmental pediatric hospital in Siem Reap. Nasopharyngeal swabs were analyzed by phenotypic and genotypic methods to detect pneumococcal serotypes and antimicrobial resistance. Invasive pneumococcal disease (IPD) data for January 2012-December 2018 were retrieved from hospital databases. Pre-PCV IPD data and pre-/post-PCV colonization data were modelled to estimate vaccine effectiveness (VE). RESULTS: Comparing 2014 with 2016-2018, and using adjusted prevalence ratios, VE estimates for colonization were 16.6% (95% confidence interval [CI] 10.6-21.8) for all pneumococci and 39.2% (95% CI 26.7-46.1) for vaccine serotype (VT) pneumococci. There was a 26.0% (95% CI 17.7-33.0) decrease in multidrug-resistant pneumococcal colonization. The IPD incidence was estimated to have declined by 26.4% (95% CI 14.4-35.8) by 2018, with a decrease of 36.3% (95% CI 23.8-46.9) for VT IPD and an increase of 101.4% (95% CI 62.0-145.4) for non-VT IPD. CONCLUSIONS: Following PCV13 introduction into the Cambodian immunization schedule, there have been declines in VT pneumococcal colonization and disease in children aged <5 years. Modelling of dominant serotype colonization data produced plausible VE estimates.

Pediatric hospitalizations attributable to rotavirus gastroenteritis among Cambodian children: Seven years of active surveillance, 2010-2016.

BACKGROUND: Each year, approximately 1,066 Cambodian children under five years old die of diarrhea, and 51% of these deaths are due to rotavirus gastroenteritis. Quantifying childhood hospitalizations caused by severe rotavirus infections is also important in demonstrating disease burden caused by this virus. The objective of this study is to update and confirm the current burden of pediatric hospitalizations attributable to rotavirus gastroenteritis among Cambodian children using seven years of continuous active, prospective surveillance from 2010 to 2016. We also characterize the circulating rotavirus genotypic strains during this period. METHODS: Active surveillance for rotavirus gastroenteritis was conducted from January 2010 through December 2016 at a national hospital in Phnom Penh, Cambodia. Children <60 months of age who were hospitalized for acute gastroenteritis (AGE) were consented and enrolled. Information on gender, age, clinical characteristics, and month of onset were collected. Stool specimens were collected and tested by enzyme immunoassay for the presence of rotavirus antigen, and genotyping was performed on rotavirus test-positive specimens to characterize predominant rotavirus strains during the surveillance period. RESULTS: Of 7007 children enrolled with AGE and having specimens collected, 3473 (50%) were attributed to rotavirus gastroenteritis. The majority of rotavirus hospitalizations occurred in children younger than two years old (92%). Year-round rotavirus transmission was observed, with seasonal peaks during the cooler, dry months between November and May. Genotypic trends in rotavirus were observed over the surveillance period; the predominant rotavirus strains changed from G1P[8] (2010-2012), to G2P[4] (2013-2014), the emergence of genotype G8P[8] in 2015, and G3P[8] in 2016. CONCLUSIONS: Rotavirus is the leading cause of severe acute gastroenteritis hospitalizations in Cambodian children under five years old, with 50% of such hospitalizations attributable to rotavirus. Over 90% of rotavirus hospitalizations occurred in children under 2 years of age. Changes in the predominant rotavirus strains occurred over time among these unvaccinated children. This information is important to understand and prioritize the current potential impacts upon child health that could be achieved through the introduction of rotavirus vaccines in Cambodia.

Molecular epidemiology of Bordetella pertussis in Cambodia determined by direct genotyping of clinical specimens.

OBJECTIVES: This study sought to determine the genotypes of circulating Bordetella pertussis, the causative agent of pertussis, in Cambodia by direct molecular typing of clinical specimens. METHODS: DNA extracts from nasopharyngeal swabs obtained from 82 pertussis patients in 2008-2016 were analyzed by multilocus variable-number tandem repeat analysis (MLVA). B. pertussis virulence-associated allelic genes (ptxA, prn, and fim3) and the pertussis toxin promoter ptxP were also investigated by DNA sequence-based typing. RESULTS: Forty-four DNA extracts (54%) yielded a complete MLVA profile, and these were sorted into 8 MLVA types (MT18, MT26, MT27, MT29, MT43, MT72, MT95, and MT200). MT27 and MT29, which are common in developed countries, were the predominant strain types (total 73%). The predominant profile of virulence-associated allelic genes was the combination of ptxP3/ptxA1/prn2/fim3A (48%). MT27 strains were detected during the entire study period, whereas MT29 strains were only found in 2014-2016. CONCLUSIONS: The B. pertussis population in Cambodia, where a whole-cell pertussis vaccine (WCV) has been continuously used, resembled those observed previously in developed countries where acellular pertussis vaccines are used. Circulating B. pertussis strains in Cambodia were distinct from those in other countries using WCVs.

Effective vaccine safety systems in all countries: a challenge for more equitable access to immunization.

Serious vaccine-associated adverse events are rare. To further minimize their occurrence and to provide adequate care to those affected, careful monitoring of immunization programs and case management is required. Unfounded vaccine safety concerns have the potential of seriously derailing effective immunization activities. To address these issues, vaccine pharmacovigilance systems have been developed in many industrialized countries. As new vaccine products become available to prevent new diseases in various parts of the world, the demand for effective pharmacovigilance systems in low- and middle-income countries (LMIC) is increasing. To help establish such systems in all countries, WHO developed the Global Vaccine Safety Blueprint in 2011. This strategic plan is based on an in-depth analysis of the vaccine safety landscape that involved many stakeholders. This analysis reviewed existing systems and international vaccine safety activities and assessed the financial resources required to operate them. The Blueprint sets three main strategic goals to optimize the safety of vaccines through effective use of pharmacovigilance principles and methods: to ensure minimal vaccine safety capacity in all countries; to provide enhanced capacity for specific circumstances; and to establish a global support network to assist national authorities with capacity building and crisis management. In early 2012, the Global Vaccine Safety Initiative (GVSI) was launched to bring together and explore synergies among on-going vaccine safety activities. The Global Vaccine Action Plan has identified the Blueprint as its vaccine safety strategy. There is an enormous opportunity to raise awareness for vaccine safety in LMIC and to garner support from a large number of stakeholders for the GVSI between now and 2020. Synergies and resource mobilization opportunities presented by the Decade of Vaccines can enhance monitoring and response to vaccine safety issues, thereby leading to more equitable delivery of vaccines worldwide.