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Epidemiologic Reviews Jan 2019The epidemiology of Middle East respiratory syndrome coronavirus (MERS-CoV) since 2012 has been largely characterized by recurrent zoonotic spillover from dromedary... (Review)
Review
The epidemiology of Middle East respiratory syndrome coronavirus (MERS-CoV) since 2012 has been largely characterized by recurrent zoonotic spillover from dromedary camels followed by limited human-to-human transmission, predominantly in health-care settings. The full extent of infection of MERS-CoV is not clear, nor is the extent and/or role of asymptomatic infections in transmission. We conducted a review of molecular and serological investigations through PubMed and EMBASE from September 2012 to November 15, 2018, to measure subclinical or asymptomatic MERS-CoV infection within and outside of health-care settings. We performed retrospective analysis of laboratory-confirmed MERS-CoV infections reported to the World Health Organization to November 27, 2018, to summarize what is known about asymptomatic infections identified through national surveillance systems. We identified 23 studies reporting evidence of MERS-CoV infection outside of health-care settings, mainly of camel workers, with seroprevalence ranges of 0%-67% depending on the study location. We identified 20 studies in health-care settings of health-care worker (HCW) and family contacts, of which 11 documented molecular evidence of MERS-CoV infection among asymptomatic contacts. Since 2012, 298 laboratory-confirmed cases were reported as asymptomatic to the World Health Organization, 164 of whom were HCWs. The potential to transmit MERS-CoV to others has been demonstrated in viral-shedding studies of asymptomatic MERS infections. Our results highlight the possibility for onward transmission of MERS-CoV from asymptomatic individuals. Screening of HCW contacts of patients with confirmed MERS-CoV is currently recommended, but systematic screening of non-HCW contacts outside of health-care facilities should be encouraged.
Topics: Adult; Aged; Asymptomatic Infections; Coronavirus Infections; Female; Humans; Male; Middle Aged; Middle East Respiratory Syndrome Coronavirus; Registries; World Health Organization
PubMed: 31781765
DOI: 10.1093/epirev/mxz009 -
Microbiology Spectrum Jun 2016Although long recognized as a human pathogen, West Nile virus (WNV) emerged as a significant public health problem following its introduction and spread across North... (Review)
Review
Although long recognized as a human pathogen, West Nile virus (WNV) emerged as a significant public health problem following its introduction and spread across North America. Subsequent years have seen a greater understanding of all aspects of this viral infection. The North American epidemic resulted in a further understanding of the virology, pathogenesis, clinical features, and epidemiology of WNV infection. Approximately 80% of human WNV infections are asymptomatic. Most symptomatic people experience an acute systemic febrile illness; less than 1% of infected people develop neuroinvasive disease, which typically manifests as meningitis, encephalitis, or anterior myelitis resulting in acute flaccid paralysis. Older age is associated with more severe illness and higher mortality; other risk factors for poor outcome have been challenging to identify. In addition to natural infection through mosquito bites, transfusion- and organ transplant-associated infections have occurred. Since there is no definitive treatment for WNV infection, protection from mosquito bites and other preventative measures are critical. WNV has reached an endemic pattern in North America, but the future epidemiologic pattern is uncertain.
Topics: Age Factors; Asymptomatic Infections; Epidemics; Humans; North America; West Nile Fever; West Nile virus
PubMed: 27337465
DOI: 10.1128/microbiolspec.EI10-0021-2016 -
Maternal & Child Nutrition Jan 2023Inadequate diet and frequent symptomatic infections are considered major causes of growth stunting in low-income countries, but interventions targeting these risk...
Inadequate diet and frequent symptomatic infections are considered major causes of growth stunting in low-income countries, but interventions targeting these risk factors have achieved limited success. Asymptomatic infections can restrict growth, but little is known about their role in global stunting prevalence. We investigated factors related to length-for-age Z-score (LAZ) at 24 months by constructing an interconnected network of various infections, biomarkers of inflammation (as assessed by alpha-1-acid glycoprotein [AGP]), and growth (insulin-like growth factor 1 [IGF-1] and collagen X biomarker [CXM]) at 18 months, as well as other children, maternal, and household level factors. Among 604 children, there was a continuous decline in mean LAZ and increased mean length deficit from birth to 24 months. At 18 months of age, the percentage of asymptomatic children who carried each pathogen was: 84.5% enterovirus, 15.5% parechovirus, 7.7% norovirus, 4.6% rhinovirus, 0.6% rotavirus, 69.6% Campylobacter, 53.8% Giardia lamblia, 11.9% malaria parasites, 10.2% Shigella, and 2.7% Cryptosporidium. The mean plasma IGF-1 concentration was 12.5 ng/ml and 68% of the children had systemic inflammation (plasma AGP concentration >1 g/L). Shigella infection was associated with lower LAZ at 24 months through both direct and indirect pathways, whereas enterovirus, norovirus, Campylobacter, Cryptosporidium, and malaria infections were associated with lower LAZ at 24 months indirectly, predominantly through increased systemic inflammation and reduced plasma IGF-1 and CXM concentration at 18 months.
Topics: Child, Preschool; Humans; Infant; Asymptomatic Infections; Biomarkers; Cryptosporidiosis; Cryptosporidium; Growth Disorders; Inflammation; Insulin-Like Growth Factor I; Malaria
PubMed: 36111423
DOI: 10.1111/mcn.13417 -
Mathematical Biosciences and... Nov 2020Asymptomatic transmission of infectious diseases has been recognized recently in several epidemics or pandemics. There is a great need to incorporate asymptomatic...
Asymptomatic transmission of infectious diseases has been recognized recently in several epidemics or pandemics. There is a great need to incorporate asymptomatic transmissions into traditional modeling of infectious diseases and to study how asymptomatic transmissions shift epidemic dynamics. In this work, we propose a compartmental model with asymptomatic transmissions for waterborne infectious diseases. We conduct a detailed analysis and numerical study with shigellosis data. Two parameters, the proportion $p$ of asymptomatic infected individuals and the proportion $k$ of asymptomatic infectious individuals who can asymptomatically transmit diseases, play major rules in the epidemic dynamics. The basic reproduction number $\mathscr{R}_{0}$ is a decreasing function of parameter $p$ when parameter $k$ is smaller than a critical value while $\mathscr{R}_{0}$ is an increasing function of $p$ when $k$ is greater than the critical value. $\mathscr{R}_{0}$ is an increasing function of $k$ for any value of $p$. When $\mathscr{R}_{0}$ passes through 1 as $p$ or $k$ varies, the dynamics of epidemics is shifted. If asymptomatic transmissions are not counted, $\mathscr{R}_{0}$ will be underestimated while the final size may be overestimated or underestimated. Our study provides a theoretical example for investigating other asymptomatic transmissions and useful information for public health measurements in waterborne infectious diseases.
Topics: Asymptomatic Infections; Basic Reproduction Number; Communicable Diseases; Epidemics; Humans; Pandemics
PubMed: 33525082
DOI: 10.3934/mbe.2021005 -
Parasites & Vectors Jan 2022Asymptomatic Leishmania infection may play an important role in the transmission of the parasite in endemic areas. At present there is no consensus on the definition of... (Review)
Review
BACKGROUND
Asymptomatic Leishmania infection may play an important role in the transmission of the parasite in endemic areas. At present there is no consensus on the definition of asymptomatic Leishmania infection, nor is there a safe and accessible gold standard test for its identification.
METHODS
This paper presents a scoping review to summarize definitions of asymptomatic Leishmania infection found in the literature, as well as to detail the approach (molecular, serological, cellular, and/or parasitological tests) used by researchers to identify this asymptomatic population. A scoping review of published and gray literature related to asymptomatic Leishmania infection was conducted; retrieved citations were screened based on predefined eligibility criteria, and relevant data items were extracted from eligible articles. The analysis is descriptive and is presented using tables, figures, and thematic narrative synthesis.
RESULTS
We conducted a screening of 3008 articles, of which 175 were selected for the full review. Of these articles, we selected 106 that met the inclusion criteria. These articles were published between 1991 and 2021, and in the last 5 years, up to 38 articles were reported. Most of the studies were conducted in Brazil (26%), Spain (14%), India (12%), Bangladesh (10%), and Ethiopia (7%). Of the studies, 84.9% were conducted in the immunocompetent population, while 15.1% were conducted in the immunosuppressed population (HIV, immunosuppressive drugs, and organ transplantation population). We report 14 different techniques and 10 strategies employed by researchers to define asymptomatic Leishmania infection in an endemic area.
CONCLUSIONS
The definition of asymptomatic Leishmania infection is not unified across the literature, but often includes the following criteria: residence (or extended stay) in a Leishmania-endemic area, no reported signs/symptoms compatible with leishmaniasis, and positive on a combination of serological, molecular, cellular, and/or parasitological tests. Caution is recommended when comparing results of different studies on the subject of asymptomatic infections, as the reported prevalence cannot be confidently compared between areas due to the wide variety of tests employed by research groups. More research on the importance of asymptomatic immunosuppressed and immunocompetent Leishmania-positive populations in leishmaniasis epidemiology is required.
Topics: Asymptomatic Infections; Endemic Diseases; Humans; Leishmaniasis; Neglected Diseases
PubMed: 34983616
DOI: 10.1186/s13071-021-05129-y -
International Journal of Infectious... Nov 2020While successful containment measures of COVID-19 in China and many European countries have led to flattened curves, case numbers are rising dramatically in other... (Review)
Review
While successful containment measures of COVID-19 in China and many European countries have led to flattened curves, case numbers are rising dramatically in other countries, with the emergence of a second wave expected. Asymptomatic individuals carrying SARS-CoV-2 are hidden drivers of the pandemic, and infectivity studies confirm the existence of transmission by asymptomatic individuals. The data addressed here show that characteristics of asymptomatic and presymptomatic infection are not identical. Younger age correlates strongly with asymptomatic and mild infections and children as hidden drivers. The estimated proportion of asymptomatic infections ranges from 18% to 81%. The current perception of asymptomatic infections does not provide clear guidance for public-health measures. Asymptomatic infections will be a key contributor in the spread of COVID-19. Asymptomatic cases should be reported in official COVID-19 statistics.
Topics: Adult; Asymptomatic Infections; Betacoronavirus; COVID-19; Child; Coronavirus Infections; Humans; Immunity, Herd; Middle Aged; Pandemics; Pneumonia, Viral; Public Health; SARS-CoV-2
PubMed: 32891737
DOI: 10.1016/j.ijid.2020.08.076 -
Sexually Transmitted Infections Nov 2021The clinical and public health relevance of widespread case finding by testing for asymptomatic chlamydia infections is under debate. We wanted to explore future... (Review)
Review
OBJECTIVES
The clinical and public health relevance of widespread case finding by testing for asymptomatic chlamydia infections is under debate. We wanted to explore future directions for chlamydia control and generate insights that might guide for evidence-based strategies. In particular, we wanted to know the extent to which we should pursue testing for asymptomatic infections at both genital and extragenital sites.
METHODS
We synthesised findings from published literature and from discussions among national and international chlamydia experts during an invitational workshop. We described changing perceptions in chlamydia control to inform the development of recommendations for future avenues for chlamydia control in the Netherlands.
RESULTS
Despite implementing a range of interventions to control chlamydia, there is no practice-based evidence that population prevalence can be reduced by screening programmes or widespread opportunistic testing. There is limited evidence about the beneficial effect of testing on pelvic inflammatory disease prevention. The risk of tubal factor infertility resulting from chlamydia infection is low and evidence on the preventable fraction remains uncertain. Overdiagnosis and overtreatment with antibiotics for self-limiting and non-viable infections have contributed to antimicrobial resistance in other pathogens and may affect oral, anal and genital microbiota. These changing insights could affect the outcome of previous cost-effectiveness analysis.
CONCLUSION
The balance between benefits and harms of widespread testing to detect asymptomatic chlamydia infections is changing. The opinion of our expert group deviates from the existing paradigm of 'test and treat' and suggests that future strategies should reduce, rather than expand, the role of widespread testing for asymptomatic chlamydia infections.
Topics: Asymptomatic Infections; Chlamydia Infections; Chlamydia trachomatis; Communicable Disease Control; Female; Humans; Infection Control; Netherlands; Pelvic Inflammatory Disease; Prevalence; Public Health
PubMed: 34045364
DOI: 10.1136/sextrans-2021-054992 -
Virology Journal Apr 2023Norovirus is a leading cause of acute gastroenteritis among children. Previous studies based on symptomatic infections indicated that mutations, rather than...
BACKGROUND
Norovirus is a leading cause of acute gastroenteritis among children. Previous studies based on symptomatic infections indicated that mutations, rather than recombination drove the evolution of the norovirus ORF2. These characteristics were found in hospital-based symptomatic infections, whereas, asymptomatic infections are frequent and contribute significantly to transmission.
METHODS
We conducted the first norovirus molecular epidemiology analysis covering both symptomatic and asymptomatic infections derived from a birth cohort study in the northern China.
RESULTS
During the study, 14 symptomatic and 20 asymptomatic norovirus infections were detected in 32 infants. Out of the 14 strains that caused symptomatic infections, 12 strains were identified as GII.3[P12], and others were GII.4[P31]. Conversely, 17 asymptomatic infections were caused by GII.4[P31], two by GII.2[P16], and one by GII.4[P16]. Regardless of symptomatic and asymptomatic infections, the mutations were detected frequently in the ORF2 region, and almost all recombination were identified in the RdRp-ORF2 region. The majority of the mutations were located around the predefined epitope regions of P2 subdomain indicating a potential for immune evasion.
CONCLUSION
The role of symptomatic as well as asymptomatic infections in the evolution of norovirus needs to be evaluated continuously.
Topics: Humans; Infant; Asymptomatic Infections; Caliciviridae Infections; Cohort Studies; East Asian People; Feces; Genotype; Molecular Epidemiology; Norovirus; Phylogeny
PubMed: 37016444
DOI: 10.1186/s12985-023-02024-z -
Journal of Infection in Developing... May 2022Despite efforts to contain and manage the SARS-CoV-2 outbreak which was declared a public health emergency of international concern in January 2020 by the World Health... (Review)
Review
Despite efforts to contain and manage the SARS-CoV-2 outbreak which was declared a public health emergency of international concern in January 2020 by the World Health Organization (WHO), the COVID-19 pandemic still remains a major global challenge. Patients who display the classical symptoms of the infection are easily identified, tested, isolated and monitored. However, many cases of infected asymptomatic patients have been documented. These patients are not easily identified even though many evidences suggest that they can spread the virus to others. How and why these COVID-19 asymptomatic presentations occur remain unclear. The many theories and views are conjectural, and supporting evidences are still needed. In this review, we described the trend in SARS-CoV-2 viral shedding and susceptibility, providing perspectives on gender differences and asymptomatic patients. We further discussed how genetics, gender, viral inoculum, and pre-existing immunity may influence asymptomatic presentations in COVID-19 infections. We hope that this article improves our understanding of asymptomatic SAR-CoV-2 infection and it sheds light on some salient areas that should be considered as the search for a potent vaccine continues.
Topics: Asymptomatic Infections; COVID-19; Humans; Pandemics; SARS-CoV-2; Virus Shedding
PubMed: 35656946
DOI: 10.3855/jidc.14721 -
Epidemics Sep 2023Throughout 2020, COVID-19 interventions prioritised symptomatic individuals despite growing evidence of pre-symptomatic and asymptomatic transmission. From the pandemic... (Review)
Review
Throughout 2020, COVID-19 interventions prioritised symptomatic individuals despite growing evidence of pre-symptomatic and asymptomatic transmission. From the pandemic we have learned that global health is slow to quantify asymptomatic disease transmission and slow to implement relevant interventions. While asymptomatic infectious periods exist for nearly all pathogens, it is frequently ignored during case finding, and there are limited research efforts to understand its potential to drive small scale outbreaks, epidemics and pandemics. We conducted a pragmatic review on 15 key pathogens including SARS-CoV-2 and Ebola to demonstrate substantial variation in terminology around asymptomatic infectious individuals, and varying proportions of asymptomatic amongst prevalent infectious cases (0-99 %) and their contribution to transmission (0-96 %). While no pattern was discernible by pathogen type (virus, bacteria, parasite) or mode of transmission (direct, indirect or mixed), there are multiple lessons to learn from previous and current control programmes. As found during the COVID-19 pandemic, overlooking asymptomatic infectious individuals can impede disease control. Improving our understanding of how asymptomatic individuals can drive epidemics can strengthen our efforts to control current pathogens, and improve our preparedness for when the next new pathogen emerges..
Topics: Humans; COVID-19; SARS-CoV-2; Pandemics; Disease Outbreaks; Communicable Diseases; Asymptomatic Infections
PubMed: 37413887
DOI: 10.1016/j.epidem.2023.100704