When should we intervene to control the 2009 influenza A(H1N1) pandemic?

Zika Virus: A Global Public Health Menace: A Comprehensive Update

Zika virus (ZIKV) is a RNA virus and belongs to genus Flavivirus and family Flaviviridae. The virus was first discovered from a febrile primate from the Zika forests of Uganda in 1947 and the first human case was documented in 1954. The nonspecific clinical manifestations of ZIKV pose diagnostic dilemmas and delays early and effective treatment. Dental professionals should have a thorough knowledge about the virus and should follow standard infection control measures as the virus has been demonstrated in various body secretions (including salivary secretions). The disease is managed by symptomatic and supportive care and no vaccine exist till date. Recent ZIKV outbreaks and increase association of microcephaly with congenital ZIKV and neurological complications (Guillain-Barré syndrome) has drawn global public health attention. The World Health Organization declared it a public health emergency of international concern in 2016. This review article provides a detailed overview on ZIKV; it is clinical and oral manifestations, diagnostic aids, differential diagnosis, preventive aspects, and management protocol.

Was mandatory quarantine necessary in China for controlling the 2009 H1N1 pandemic?

The Chinese government enforced mandatory quarantine for 60 days (from 10 May to 8 July 2009) as a preventative strategy to control the spread of the 2009 H1N1 pandemic. Such a prevention strategy was stricter than other non-pharmaceutical interventions that were carried out in many other countries. We evaluated the effectiveness of the mandatory quarantine and provide suggestions for interventions against possible future influenza pandemics. We selected one city, Beijing, as the analysis target. We reviewed the epidemiologic dynamics of the 2009 H1N1 pandemic and the implementation of quarantine measures in Beijing. The infectious population was simulated under two scenarios (quarantined and not quarantined) using a deterministic Susceptible-Exposed-Infectious-Recovered (SEIR) model. The basic reproduction number R0 was adjusted to match the epidemic wave in Beijing. We found that mandatory quarantine served to postpone the spread of the 2009 H1N1 pandemic in Beijing by one and a half months. If mandatory quarantine was not enforced in Beijing, the infectious population could have reached 1,553 by 21 October, i.e., 5.6 times higher than the observed number. When the cost of quarantine is taken into account, mandatory quarantine was not an economically effective intervention approach against the 2009 H1N1 pandemic. We suggest adopting mitigation methods for an influenza pandemic with low mortality and morbidity.

Enhancement of collective immunity in Tokyo metropolitan area by selective vaccination against an emerging influenza pandemic

Vaccination is a preventive measure against influenza that does not require placing restrictions on social activities. However, since the stockpile of vaccine that can be prepared before the arrival of an emerging pandemic strain is generally quite limited, one has to select priority target groups to which the first stockpile is distributed. In this paper, we study a simulation-based priority target selection method with the goal of enhancing the collective immunity of the whole population. To model the region in which the disease spreads, we consider an urban area composed of suburbs and central areas connected by a single commuter train line. Human activity is modelled following an agent-based approach. The degree to which collective immunity is enhanced is judged by the attack rate in unvaccinated people. The simulation results show that if students and office workers are given exclusive priority in the first three months, the attack rate can be reduced from [Formula: see text] in the baseline case down to 1-2%. In contrast, random vaccination only slightly reduces the attack rate. It should be noted that giving preference to active social groups does not mean sacrificing those at high risk, which corresponds to the elderly in our simulation model. Compared with the random administration of vaccine to all social groups, this design successfully reduces the attack rate across all age groups.

Dynamics of a model with quarantine-adjusted incidence and quarantine of susceptible individuals

A new deterministic model for the spread of a communicable disease that is controllable using mass quarantine is designed. Unlike in the case of the vast majority of prior quarantine models in the literature, the new model includes a quarantine-adjusted incidence function for the infection rate and the quarantine of susceptible individuals suspected of being exposed to the disease (thereby making it more realistic epidemiologically). The earlier quarantine models tend to only explicitly consider individuals who are already infected, but show no clinical symptoms of the disease (i.e., those latently-infected), in the quarantine class (while ignoring the quarantine of susceptible individuals). In reality, however, the vast majority of people in quarantine (during a disease outbreak) are susceptible. Rigorous analysis of the model shows that the assumed imperfect nature of quarantine (in preventing the infection of quarantined susceptible individuals) induces the phenomenon of backward bifurcation when the associated reproduction threshold is less than unity (thereby making effective disease control difficult). For the case when the efficacy of quarantine to prevent infection during quarantine is perfect, the disease-free equilibrium is globally-asymptotically stable when the reproduction threshold is less than unity. Furthermore, the model has a unique endemic equilibrium when the reproduction threshold exceeds unity (and the disease persists in the population in this case).

The characteristics of imported cases and the effectiveness of outbreak control strategies of pandemic influenza A (H1N1) in China

The aim of this article was to describe the epidemiological characteristics of imported cases of pandemic influenza A (H1N1) and to assess the effectiveness of public health intervention measures in Beijing, China. Data on imported cases were collected via border entry screening, influenza-like illness screening in hospitals, medical follow-up of travelers from overseas, and quarantined close contacts. The characteristics of these cases were investigated. Pharyngeal swabs were collected and tested using polymerase chain reaction. A total of 609 imported cases were confirmed in Beijing from May 16 to September 30, 2009. Subjects aged <20 years accounted for 47.3%, and females represented 49.1%. Most cases were from North America and South America (27.3%). There were 21.8%, 18.7%, 3.1%, and 56.3% of cases detected separately via border entry screening, quarantined close contacts, medical follow-up of travelers from overseas, and influenza-like illness screening in hospitals, respectively. The 4 strategies were able to detect the cases efficiently but the use of resources was high.