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. 2013 Dec 23;8(3):309–316. doi: 10.1111/irv.12226

A systematic review of studies on forecasting the dynamics of influenza outbreaks

Elaine O Nsoesie a,b,c, John S Brownstein a,b,d, Naren Ramakrishnan e, Madhav V Marathe c,e
PMCID: PMC4181479  PMID: 24373466

Abstract

Forecasting the dynamics of influenza outbreaks could be useful for decision-making regarding the allocation of public health resources. Reliable forecasts could also aid in the selection and implementation of interventions to reduce morbidity and mortality due to influenza illness. This paper reviews methods for influenza forecasting proposed during previous influenza outbreaks and those evaluated in hindsight. We discuss the various approaches, in addition to the variability in measures of accuracy and precision of predicted measures. PubMed and Google Scholar searches for articles on influenza forecasting retrieved sixteen studies that matched the study criteria. We focused on studies that aimed at forecasting influenza outbreaks at the local, regional, national, or global level. The selected studies spanned a wide range of regions including USA, Sweden, Hong Kong, Japan, Singapore, United Kingdom, Canada, France, and Cuba. The methods were also applied to forecast a single measure or multiple measures. Typical measures predicted included peak timing, peak height, daily/weekly case counts, and outbreak magnitude. Due to differences in measures used to assess accuracy, a single estimate of predictive error for each of the measures was difficult to obtain. However, collectively, the results suggest that these diverse approaches to influenza forecasting are capable of capturing specific outbreak measures with some degree of accuracy given reliable data and correct disease assumptions. Nonetheless, several of these approaches need to be evaluated and their performance quantified in real-time predictions.

Keywords: Compartmental models, individual-based models, infectious diseases, influenza forecasting, pandemics, time series models

Introduction

An extensive body of the literature exists on mathematical and computational models for studying the spatio-temporal dynamics of influenza outbreaks. A main purpose of some of these models is to inform public policy regarding the selection and allocation of public health interventions and resources during a pandemic.1 Reliable forecasts of measures such as peak time, peak height, and magnitude during an outbreak would inform public health practitioners and healthcare workers on when to expect a surge in demand for healthcare resources and infrastructure and the overall expected public health impact of an outbreak. Although timely forecasts of these measures would be beneficial, making reliable predictions during an outbreak remains a public health challenge.

Several of the major approaches applied to modeling influenza transmission and dynamics have been applied to the forecasting of influenza outbreaks (see Table 1 for brief descriptions).2–5 These models have been reviewed in the context of pandemic preparedness, control, and mitigation.1,6–8 However, there are no reviews discussing the application of these models to the forecasting of influenza outbreaks. The goal of this paper is therefore to present a systematic review of studies that have discussed approaches for influenza forecasting at the local, regional, national, or global level. The main aims are to (i) summarize existing approaches to influenza forecasting, (ii) present differences in measures of accuracy and evaluate the degree to which various performance measures are met, (iii) discuss limitations in the data sources, and parameter estimation that impede forecasting during outbreaks. The motivation of this paper is to inform further research on influenza forecasting and provide researchers and public health practitioners with a summary of the accomplishments and limitations in influenza forecasting.

Table 1.

Model description, advantages, and limitations

Approach Description Advantages Limitations
Time series models The Box-Jenkins approach, specifically the autoregressive integrated moving average (ARIMA) model is typically used. ARIMA models assume that future values can be predicted based on past observations. ARIMA models capture lagged relationships that usually exist in periodically collected data. In addition, temporal dependence can also be adequately represented in models that are capable of capturing trend and periodic changes. Influenza activity is not consistent from season to season, which could impose limitations to ARIMA models, especially during pandemics, which can occur off-season.
Approaches in meteorology (Method of analogs) The method of analogs is a nonparametric forecasting approach in meteorology. Forecasting is based on matching current influenza patterns to patterns of historical outbreaks. The onset of seasonal influenza epidemics varies from year to year in most countries in the Northern hemisphere. As the method of analogs is nonparametric, implying it makes no assumptions on underlying distributions or seasonality, it can sometimes outperform methods (such as ARIMA) that include a seasonal component. Limitations exist on the sensitivity to forecasts and difficulty in finding similar patterns from historical outbreaks.
Compartmental models These models divide the population into compartments based on disease states and define rates at which individuals move between compartments. Examples include susceptible–infectious–recovered (SIR) and susceptible–exposed–infectious–recovered (SEIR) models. Compartmental models are attractive due to their simplicity and well-studied behavior. These models are typically extended by defining multiple compartments to introduce subpopulations, including a branching process, or used in combination with other approaches, such as particle filtering, for influenza forecasting. The usual fully mixed, homogenous population assumption fails to capture the differences in contact patterns for different age groups and environments.
Agent-based models These are computational systems in which the global behavior emerges due to individual behavior of well-defined entities called agents, which interact with other entities and their environment based on specific rules. These models have been used to address questions relating to the impact of control measures and changes in individual behavior during an outbreak. They can therefore enable the forecasting of influenza dynamics under different intervention and resource allocation scenarios. One major difficulty in applying these models is the rather circumscribed assumptions under which they operate, compounded by our limitations in understanding the modeling of human behavior via contact networks.
Metapopulation models Populations in the model are represented in structured and separated discrete patches and subpopulations interact through migration. Epidemic dynamics can be described within patches using clearly defined disease states such as in compartmental models. The detailed mobility networks used in some of these models can enable reliable description of the diffusion pattern of an ongoing epidemic. These models have also been used to evaluate the effectiveness of various measures for controlling influenza epidemics. Similar to agent-based models, there exist the challenge of empirically justifying modeling suppositions and defining parameters.
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Article selection and evaluation

The scope of this review included studies designed to predict influenza dynamics at the local, regional, national, or global level. First, we searched PubMed and Google Scholar for articles on influenza forecasting. A search for (“influenza, human”[MeSH Terms] OR (“influenza”[All Fields] AND “human”[All Fields]) OR “human influenza”[All Fields] OR “influenza”[All Fields]) AND (“forecasting”[All Fields] OR “forecasting”[MeSH Terms]) on PubMed retrieved 239 articles. Replacing “forecasting” with “prediction” in the previous search criteria resulted in 370 articles. A Google Scholar search for “influenza forecasting” retrieved 12 000 articles. Next, we focused on articles with “influenza” and “forecasting” or “prediction” in the titles and/or abstracts. Third, we selected articles that mentioned influenza forecasting as one of the aims in the abstract. After eliminating non-English articles, 35 articles remained. Lastly, we excluded articles focusing on topics such as forecasting emergency department visits, which have already been covered in a previous review.33 The study is therefore based on the remaining 16 articles, which included both prospective and retrospective studies. We group and present studies based on measures predicted.

Results

We acknowledge that there were numerous endeavors made by various research groups and organizations toward real-time forecasting of the 2009 H1N1 pandemic. However, for several of these endeavors, we were unable to find published descriptions of the methodology used in forecasting. A brief description of the modeling approaches in the sixteen selected articles, in addition to advantages and limitations to using these methods for influenza forecasting can be found in Table 1. In Table 2, we present a summary of study characteristics.

Table 2.

Summary of study characteristics

Author Publication year Date type Data scale Data range Location Method Predicted measure Measure of accuracy
Longini et al.15 1986 ILI Weekly 1968–1969 52 cities Mathematical model defined on a continuous state space in discrete time ILI across 425 days and peak period Deviation from ILI estimated based on WHO reports
Aguirre & Gonzalez9 1992 ILI Daily 1988 Havana, Cuba Mathematical model defined on a continuous state space in discrete time Daily ILI, peak, and duration Correlation and statistical tests
Viboud et al.10 2003 ILI Weekly 1984–2002 France & Administrative Districts Method of analogs Weekly ILI Correlation and RMSE
Hall et al.3 2006 ILI and deaths attributable to influenza Weekly 1968–1970, 1918–1919 & 1957–1958 United Kingdom Deterministic mass action model Timing and amplitude of peak, duration, and magnitude Error and time difference
Polgreen et al.13 2007 Influenza activity Weekly 2004–2005 Iowa, USA Prediction markets Weekly activity based on CDC's color coded system Proportion predicting correct color code
Andersson et al.20 2008 LCI cases Weekly 1999–2006 Sweden Regression model and prediction rules Peak timing and height Error and time difference
Jiang et al.11 2009 ILI and deaths attributable to influenza Daily 2006 USA Bayesian network Epidemic curve Correlation and error
Towers & Feng16 2009 Influenza case count data Weekly 2009 USA SIR model Peak time and attack rate Confidence intervals
Soebiyanto et al.12 2010 LCI cases Weekly 2005–2008 Hong Kong & Maricopa county, AZ, USA ARIMA model Weekly case counts RMSE
Ong et al.4 2010 ILI Weekly 2009 Singapore SEIR model with particle filtering Weekly case counts, peak timing, and duration Error
Chao et al.2 2010 CDC influenza case estimates and estimates of vaccine availability and distribution None 2009–2010 USA & LA County, USA Epidemic simulation model based on a synthetic population Peak timing and magnitude Predicted range
Nishiura14 2011 Influenza cases Weekly 2009–2010 Japan Discrete time stochastic model Weekly case counts Prediction intervals
Shaman & Karspeck18 2012 Google Flu Trends Weekly 2003–2008 New York City, USA SIRS model with ensemble adjustment Kalman filter Peak timing Posterior estimates and deviation
Tizzoni et al.5 2012 ILI, ARI incidence, LCI Weekly 2009 48 countries Metapopulation stochastic epidemic model Peak timing and attack rate Confidence intervals and time difference
Hyder et al.21 2013 LCI Weekly 1998–2006 Montreal, QC, Canada Individual-based model Peak timing, peak intensity, and epidemic duration Error and time difference
Nsoesie et al.19 2013 Google Flu Trends Weekly 2004–2005, 2007–2008 & 2012–2013 Seattle, WA, USA Individual-based model Peak timing Confidence intervals and deviation
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LCI, laboratory confirmed influenza; ILI, influenza-like illness; ARI, acute respiratory infection; ARIMA, autoregressive integrated moving average; RMSE, root-mean-squared-error.

Measures predicted

The articles in Table 2 aimed to either forecast a single measure or multiple measures. Typical measures predicted included epidemic trend, duration, peak timing, peak height, and magnitude. For simplicity, we grouped these measures into magnitude, peak timing and intensity, and duration. We discuss differences in measures of accuracy, which appeared to depend on the modeling approach and the measure predicted.

Magnitude

Eleven of the sixteen studies forecasted the expected magnitude, daily or weekly influenza activity based on data on confirmed laboratory cases, and/or influenza-like illness. As noted, measures of accuracy differed across studies. Aguirre and Gonzalez,9 Viboud et al.10, and Jiang et al.11 used correlation coefficients to evaluate accuracy in daily and weekly forecasts of influenza activity. The correlation coefficient between the predicted and observed values ranged from 58% to 93·5% depending on the length of the forecasts. Although useful in comparing data trends, correlation coefficients do not measure the closeness of the predicted to the observed values.

On the other hand, the closeness of the predicted to the observed data could be evaluated using different measures of error. For instance, Jiang et al.11 observed different percent errors depending on when prediction was made. Prediction of the epidemic curve made a few days from the peak had an estimated 10·8% percent error, which was much lower than the 91·6% percent error observed using nine fewer data points. Similarly, Soebiyanto et al.12 presented several ARIMA models and evaluated accuracy based on the root-mean-squared-error (RMSE) of one-step-ahead predictions. They also considered the effects of including environmental variables such as humidity and temperature. The preferred models had RMSE approximately in the range of 0·47–0·61. Alternatively, Polgreen et al.13 presented a prediction market for influenza forecasting and assessed accuracy based on the proportion of correct predictions of a particular color code representing a level of influenza activity. The prediction markets yielded correct predictions 71%, 50%, and 43% of the time by the end of the target week, 1 week in advance, and 2 weeks in advance, respectively.

Some of the studies evaluated accuracy using prediction and confidence intervals. For instance, the true incidences were included in the 95% prediction intervals for epidemic forecasts made at the peak and after the peak for the 2009 pandemic in Japan by Nishiura.14 Predictions made for the 1968–1969 pandemic, also known as the Hong Kong flu, were presented graphically and assessed to have overlapped with the observed data in 42 of 44 cities.15 Influenza case estimates made by Chao et al.2 also overlapped with the estimated ranges from the US CDC.

Most of the previous methods were evaluated retrospectively or published after the 2009 pandemic. Towers and Feng16 presented forecasts of the 2009 pandemic in the US as it unfolded. They predicted the proportion of the infected population at 63% without vaccination and 57% with the inclusion of the planned vaccination scheme in the model. The 57% estimate was much higher than estimates presented by the CDC. However, real-time predictions of outbreak dynamics are extremely difficult compared with retrospective evaluations due to limitations in data and difficulty in obtaining reliable parameter estimates as we later discuss.

Peak timing and intensity

Methods applied to forecasting peak time have been shown to perform reasonably well when reliable data and parameter estimates are used. For instance, during the 2009 pandemic, Towers and Feng16 predicted that the peak would be observed in the US toward the end of October in week 42 with 95% confidence intervals between weeks 39 and 43. According to CDC reports,17 H1N1 peaked in the US during the second week of October. Ong et al.4 also predicted a few weeks in advance that the 2009 pandemic in Singapore would peak at the start of August. However, the peak height was overestimated. Chao et al.2 also showed that simulated 2009 H1N1 epidemic for LA County peaked at about the same time (mid-November) as reported by the LA county Department of Public Health.

Using web-based estimates of influenza activity, Shaman and Karspeck18 and Nsoesie et al.19 retrospectively illustrated that peak time could be predicted as early as 7 and 6 weeks, respectively, before the actual peak for seasonal outbreaks of influenza in the US. Unfortunately, web-based estimates do not always capture trends in influenza activity and could therefore distort accuracy of predicted outcomes.

Studies published before the 2009 pandemic also had some success. For example, the model discussed by Longini et al.15 retrospectively estimated the peak time for the 1968–1969 Hong Kong influenza pandemic within the 4-day epidemic peak period for 32% of the cities for which morbidity data were available. Using the same model as that discussed in, Longini et al.,15 Aguirre and Gonzalez9 predicted the 1988 influenza epidemic in Havana, Cuba to peak on March 15th. However, the true peak was observed on March 1st, implying a deviation of approximately 2 weeks. Additionally, Hall et al.3 showed that pandemic amplitude could be predicted to within 20% and peak timing within a week in retrospective evaluations using ILI and mortality data for three pre-2009 pandemics. Andersson et al.20 observed a median error of 0·9 weeks and a median deviation of approximately 28% for predictions of the peak time and peak height, respectively, for seven seasonal outbreaks (from 1999 to 2006) in Sweden.

Compared with the other metrics, the peak time appears to be the easiest to forecast. However, forecasting the peak height is more complex and is usually over- or underestimated.

Duration

Outbreak duration is typically defined in terms of baseline levels of infection. Compared with the other metrics, fewer papers have focused on predicting outbreak duration. Aguirre and Gonzalez9 correctly predicted the end of the 1988 epidemic in Havana, Cuba. Based on a retrospective study of three pandemic events, Hall et al.3 predicted pandemic durations within 2 weeks of the actual duration. In contrast, Hyder et al.21 retrospectively illustrated that duration could be underestimated by as little as 2 weeks and as much as 14 weeks for some influenza seasons.

The previously discussed results suggest that reliable forecast of influenza dynamics is possible. However, diversity in modeling approaches, and differences in measures of accuracy makes forecast comparison difficult.

Discussion

The number of new infections at any time during an influenza outbreak depends on several biological, behavioral, and environmental factors that influence the transmission of influenza viruses.22 These factors include immunity, virulence factors, contact type and patterns, and climatic conditions that influence viral survival. The inclusion of these parameters in models for influenza forecasting could improve forecast accuracy. However, in addition to the difficulty of estimating true influenza incidence from laboratory confirmed cases and ILI, estimating transmission and severity parameters during pandemics remains a challenge.23 We discuss these challenges.

Parameter estimation

Unlike seasonal outbreaks of influenza, pandemics are rare and usually result from novel influenza viruses. A meager understanding of the natural history of the virus hinders the estimation of transmission and severity parameters in real time. Estimating the transmission potential of an emerging infection early on is important as it would help determine whether control measures should be varied and whether more stringent measures are required to control or mitigate an outbreak.24,25 In several publications, the transmissibility and natural history of influenza have been estimated at the household, school, or community level using observational data.26,27 However, data are typically unavailable or incomplete during the early stages of an outbreak resulting from a novel influenza virus.

The disease severity, which is another important measure, is commonly estimated based on case fatality, hospitalization rates, and clinical attack rates. Approximations of case fatality and hospitalization rates could be underestimated due to subclinical and asymptomatic cases. Although clinical attack rates could be estimated at the community level, data on laboratory-diagnosed cases might be delayed. Nevertheless, studies conducted during the 2009 pandemic suggested that estimates of severity and transmissibility improved as the pandemic progressed.27,28

Data

Traditional systems for monitoring ILI and acute respiratory tract infections rely on reports from general practices, family doctor clinics, diagnostic test laboratories, and public health departments for influenza surveillance.3,4,14 There is typically 1–2 week lag(s) in the publishing of reports, and reported cases are sometimes retrospectively adjusted. Additionally, the exact number of influenza cases is unobtainable due to unreported cases and asymptomatic infections.

In view of the challenge in obtaining timely influenza surveillance data from conventional methods, alternative sources of data such as Google Flu Trends have been considered. Google Flu Trends29 attempts to provide estimates of influenza activity based on Internet search data. Other data sources, such as flu prescription drug sales, nonprescription medication sales, school absenteeism, ILI symptom reports on social media, and emergency department chief complaints, have also been evaluated as proxies for capturing ongoing influenza trends.

Although these novel data sources provide information in near real time, which is useful for daily or weekly forecasts of influenza activity,18,19,30 there are several limitations to using these data. Limitations include reduced application in low-resource countries and deviations from influenza patterns presented by traditional surveillance systems. For example, Cook et al.31 compared H1N1-related search queries on Google Insight to traditional surveillance data for the H1N1 pandemic in Singapore. The outbreak peaked in August 2009; however, search query data suggested an earlier peak and also decreased to about 20% of the search volume around the epidemic's peak time. Furthermore, during the 2012–2013 influenza season, estimates of influenza activity provided by Google Flu Trends did not match estimates provided by traditional influenza surveillance systems.32 The challenge therefore remains for timely estimates of influenza activity for weekly forecasts at different geographical levels.

Conclusion

Reliable forecasts of measures such as trend, peak height, and peak time during influenza outbreaks would inform healthcare practitioners on when to expect changes in demand for healthcare resources. Practitioners could therefore prepare for surges in influenza cases by acquiring the necessary resources (such as vaccines and antiviral treatments) and alerting essential personnel (such as nurses and doctors). However, forecasts must be interpretable to be useful. It is therefore important for studies to clearly define the predicted event, the temporal and spatial applicability of the approach, quantify the likelihood of the event either based on a probabilistic statement or relative to other similar events, and highlight the limitations (see Figure 1). In addition, defining a global measure of accuracy for evaluating the correctness of various forecasting methods would ease the process of forecast comparison. Lastly, several of the studies discussed in this review are retrospective. The challenge therefore remains in evaluating and quantifying the performance of these methods in real time.

Figure 1.

Figure 1

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Summary of forecasting process.

Acknowledgments

This work is supported by the Intelligence Advanced Research Projects Activity (IARPA) via Department of Interior National Business Center (DoI/NBC) contract number D12PC000337, and the US Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright annotation thereon.

Disclaimer

The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of IARPA, DoI/NBC, or the US Government.

References

  • 1.Lee VJ, Lye DC, Wilder-Smith A. Combination strategies for pandemic influenza response – a systematic review of mathematical modeling studies. BMC Med. 2009;7:76. doi: 10.1186/1741-7015-7-76. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 2.Chao DL, Matrajt L, Basta NE, et al. Planning for the control of pandemic influenza A (H1N1) in Los Angeles County and the United States. Am J Epidemiol. 2011;173:1121–1130. doi: 10.1093/aje/kwq497. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 3.Hall IM, Gani R, Hughes HE, Leach S. Real-time epidemic forecasting for pandemic influenza. Epidemiol Infect. 2007;135:372–385. doi: 10.1017/S0950268806007084. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Ong JBS, Chen MIC, Cook AR, et al. Real-time epidemic monitoring and forecasting of H1N1-2009 using influenza-like illness from general practice and family doctor clinics in Singapore. PLoS One. 2010;5:e10036. doi: 10.1371/journal.pone.0010036. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 5.Tizzoni M, Bajardi P, Poletto C, et al. Real-time numerical forecast of global epidemic spreading: case study of 2009 A/H1N1pdm. BMC Med. 2012;10:165. doi: 10.1186/1741-7015-10-165. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 6.Arino J, Bauch C, Brauer F, et al. Pandemic influenza: modelling and public health perspectives. Math Biosci Eng. 2011;8:1–20. doi: 10.3934/mbe.2011.8.1. [DOI] [PubMed] [Google Scholar]
  • 7.Carrasco LR, Jit M, Chen MI, Lee VJ, Milne GJ, Cook AR. Trends in parameterization, economics and host behaviour in influenza pandemic modelling: a review and reporting protocol. Emerg Themes Epidemiol. 2013;10:3. doi: 10.1186/1742-7622-10-3. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 8.Coburn BJ, Wagner BG, Blower S. Modeling influenza epidemics and pandemics: insights into the future of swine flu (H1N1) BMC Med. 2009;7:30. doi: 10.1186/1741-7015-7-30. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 9.Aguirre A, Gonzalez E. The feasibility of forecasting influenza epidemics in Cuba. Mem Inst Oswaldo Cruz. 1992;87:429–432. doi: 10.1590/s0074-02761992000300014. [DOI] [PubMed] [Google Scholar]
  • 10.Viboud C, Boëlle PY, Carrat F, Valleron AJ, Flahault A. Prediction of the spread of influenza epidemics by the method of analogues. Am J Epidemiol. 2003;158:996–1006. doi: 10.1093/aje/kwg239. [DOI] [PubMed] [Google Scholar]
  • 11.Jiang X, Wallstrom G, Cooper GF, Wagner MM. Bayesian prediction of an epidemic curve. J Biomed Inform. 2009;42:90–99. doi: 10.1016/j.jbi.2008.05.013. [DOI] [PubMed] [Google Scholar]
  • 12.Soebiyanto RP, Adimi F, Kiang RK. Modeling and predicting seasonal influenza transmission in warm regions using climatological parameters. PLoS One. 2010;5:e9450. doi: 10.1371/journal.pone.0009450. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 13.Polgreen PM, Nelson FD, Neumann GR. Use of prediction markets to forecast infectious disease activity. Clin Infect Dis. 2007;44:272–279. doi: 10.1086/510427. [DOI] [PubMed] [Google Scholar]
  • 14.Nishiura H. Real-time forecasting of an epidemic using a discrete time stochastic model: a case study of pandemic influenza (H1N1-2009) Biomed Eng Online. 2011;10:15. doi: 10.1186/1475-925X-10-15. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 15.Longini IM, Fine PEM, Thacker SB. Predicting the global spread of new infectious agents. Am J Epidemiol. 1986;123:383–391. doi: 10.1093/oxfordjournals.aje.a114253. [DOI] [PubMed] [Google Scholar]
  • 16.Towers S, Feng Z. Pandemic H1N1 influenza: predicting the course of a pandemic and assessing the efficacy of the planned vaccination programme in the United States. Euro Surveill. 2009;14:19358. [PubMed] [Google Scholar]
  • 17.CDC. Updated CDC estimates of 2009 H1N1 influenza cases, hospitalizations and deaths in the United States, April 2009-April 10, 2010 http://www.cdc.gov/h1n1flu/estimates_2009_h1n1.htm (Accessed on 16 March 2012)
  • 18.Shaman J, Karspeck A. Forecasting seasonal outbreaks of influenza. Proc Natl Acad Sci U S A. 2012;109:20425–20430. doi: 10.1073/pnas.1208772109. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 19.Nsoesie E, Marathe M, Brownstein JS. Forecasting peaks of seasonal influenza epidemics. PLoS Curr. 2013;5 doi: 10.1371/currents.outbreaks.bb1e879a23137022ea79a8c508b030bc. doi: 10.1371/currents.outbreaks.bb1e879a23137022ea79a8c508b030bc. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 20.Andersson E, Kühlmann-Berenzon S, Linde A, Schiöler L, Rubinova S, Frisén M. Predictions by early indicators of the time and height of the peaks of yearly influenza outbreaks in Sweden. Scand J Public Health. 2008;36:475–482. doi: 10.1177/1403494808089566. [DOI] [PubMed] [Google Scholar]
  • 21.Hyder A, Buckeridge DL, Leung B. Predictive validation of an influenza spread model. PLoS One. 2013;8:e65459. doi: 10.1371/journal.pone.0065459. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22.Grassly NC, Fraser C. Mathematical models of infectious disease transmission. Nat Rev Microbiol. 2008;6:477–487. doi: 10.1038/nrmicro1845. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 23.Lipsitch M, Finelli L, Heffernan RT, Leung GM, Redd SC. Improving the evidence base for decision making during a pandemic: the example of 2009 influenza A/H1N1. Biosecur Bioterror. 2011;9:89–115. doi: 10.1089/bsp.2011.0007. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 24.Pourbohloul B, Meyers LA, Skowronski DM, Krajden M, Patrick DM, Brunham RC. Modeling control strategies of respiratory pathogens. Emerg Infect Dis. 2005;11:1249–1256. doi: 10.3201/eid1108.040449. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 25.Wallinga J, Teunis P. Different epidemic curves for severe acute respiratory syndrome reveal similar impacts of control measures. Am J Epidemiol. 2004;160:509–516. doi: 10.1093/aje/kwh255. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 26.Cauchemez S, Carrat F, Viboud C, Valleron AJ, Boëlle PY. A Bayesian MCMC approach to study transmission of influenza: application to household longitudinal data. Stat Med. 2004;23:3469–3487. doi: 10.1002/sim.1912. [DOI] [PubMed] [Google Scholar]
  • 27.Fraser C, Donnelly CA, Cauchemez S, et al. Pandemic potential of a strain of influenza A (H1N1): early findings. Science. 2009;324:1557–1561. doi: 10.1126/science.1176062. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 28.Pourbohloul B, Ahued A, Davoudi B, et al. Initial human transmission dynamics of the pandemic (H1N1) 2009 virus in North America. Influenza Other Respir Viruses. 2009;3:215–222. doi: 10.1111/j.1750-2659.2009.00100.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 29.Ginsberg J, Mohebbi MH, Patel RS, et al. Detecting influenza epidemics using search engine query data. Nature. 2009;457:1012–1014. doi: 10.1038/nature07634. [DOI] [PubMed] [Google Scholar]
  • 30.Dugas AF, Jalalpour M, Gel Y, et al. Influenza forecasting with Google Flu Trends. PLoS One. 2013;8:e56176. doi: 10.1371/journal.pone.0056176. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 31.Cook AR, Chen MIC, Lin RTP. Internet search limitations and pandemic influenza, Singapore. Emerg Infect Dis. 2010;16:1647–1649. doi: 10.3201/eid1610.100840. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 32.Butler D. When Google got flu wrong. Nature. 2013;494:155–156. doi: 10.1038/494155a. [DOI] [PubMed] [Google Scholar]
  • 33.Wargon M, Guidet B, Hoang TD, Hejblum G. A systematic review of models for forecasting the number of emergency department visits. Emerg Med J. 2009;26:395–399. doi: 10.1136/emj.2008.062380. [DOI] [PubMed] [Google Scholar]

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