Telephone Survey to Assess Influenza-like Illness, United States, 2006

This method offers a potentially feasible means to monitor patients at home.

T he US Department of Health and Human Services (DHHS), Centers for Disease Control and Prevention (CDC), and other government agencies have been working to strengthen public health systems and improve strategies for monitoring and controlling pandemic infl uenza. According to the US Homeland Security Council's National Strategy for Pandemic Infl uenza Implementation Plan, "... the public health community must have situational awareness of the evolution of disease that can only come from connectivity to the emergency departments and other acute care settings where patients with infl uenza are presenting.
The interpandemic period presents an opportunity to establish and test these relationships" (1).
CDC currently supports the infl uenza surveillance reporting systems listed in Table 1 (2,3). Surveillance goals of the DHHS pandemic infl uenza plan are to 1) provide an early-warning system; 2) detect increases in infl uenza-like illness (ILI) at the local level; 3) monitor the impact of infl uenza on health (e.g., track outpatient visits, hospitalizations, and deaths); 4) track trends in infl uenza disease activity; and 5) identify severely affected populations (3). Outpatient surveillance of ILI is emphasized at the national, regional, and state levels through CDC's Sentinel Provider Network (SPN), which gathers and summarizes infl uenza illness surveillance reports from ≈2,300 healthcare providers nationwide (2). CDC plans to analyze daily reports of ambulatory patients with infl uenza that are accessed through the BioSense surveillance system (4,5) and use existing emergency department symptom-monitoring systems (2). This approach will strengthen systems that support situational awareness of infl uenza outbreaks, support geographic completeness and frequency of reporting, and ensure sustainable collection of ILI data during a pandemic.
The DHHS Pandemic Infl uenza Plan notes that "most patients with pandemic infl uenza will be able to remain at home during the course of their illness and can be cared for by other family members or others who live in the household" (6). Local health districts, although responsible for monitoring the care of these at-home patients and maintaining continuity of services, may be too overwhelmed to do so. Because of the expected high demand for medical services during a pandemic infl uenza emergency, SPN providers may also be overwhelmed, may have diffi culty fi nding time to report outpatient ILI status in a timely manner, and Telephone Survey to Assess  Infl uenza-like Illness,  United States, 2006 may be unable to monitor ILI patients at home (4). Inadequate surveillance will result in reduced situational awareness at local, state, and federal levels. Currently, none of the functioning federal public health systems has plans in place to identify or monitor the health status of at-home patients with ILI symptoms. We investigated whether a national telephone survey system would be feasible to fi ll the gap in surveillance. To determine whether national and local situational awareness of infl uenza could be improved by monitoring at-home patients in a systematic way, we partnered with a public opinion research company to administer and analyze the results of a telephone survey. We report the results of that survey.

Methods
Using national pandemic infl uenza planning documents, CDC guidance, and the recent medical literature, we developed a telephone survey questionnaire ( Table 2) that asked "Do you have the fl u?" and questions about symptoms such as fever, cough, and sore throat. This design allows comparison of the survey data with the SPN's defi nition of ILI (i.e., fever [>100°F (37.8°C)] and cough and/or sore throat in the absence of a known cause other than infl uenza). Possible risk factors for exposure to novel avian infl uenza strains through live poultry (7), foreign travel (8,9), and cats (10) were also addressed in the survey.
To explore the feasibility of using this telephone survey, we partnered with Zogby International (Utica, NY, USA) (11), a private public opinion research company experienced at collecting extensive demographic and socioeconomic information through nationwide telephone surveys. A protocol to perform telephone surveys was   *Questions A-C were asked of all adults taking the telephone survey. Only respondents who answered "yes" to Question C were asked Question C.1; only respondents who answered "yes" to C.1 were asked the follow-up questions C.1.1 through C. 1.10. and October 12 (week 41). These dates were selected as a convenience sample based upon having received necessary IRB approvals and having the availability of telephone survey capacity by our telephone surveying partners. Telephone numbers for the surveys were randomly selected from commercially available national data sets of residential directory-listed telephone numbers. The probability of selection for the telephone survey was adjusted to be proportional to population sizes within area codes and telephone exchanges. As many as 6 calls were made to reach a sampled phone number, and the procedures did not result in the same telephone numbers selected to be surveyed for each subsequent month.
One adult from each randomly sampled household was asked to answer the survey questionnaire by telephone. All interviews were conducted by Zogby International's general interviewers, who are monitored by supervisors to assess adherence to surveying standards. For this study, the interviewer-to-supervisor ratio was 12:1. Quality control checks of interviewer performance were conducted on 10% of all calls. The survey was performed according to a protocol created by medical researchers at the University of Texas Health Science Center at Houston and approved by the university's Institutional Review Board. Survey results were tabulated, analyzed, and correlated by the study authors with nationwide infl uenza surveillance reports from CDC (Table 1)

Results
Of 8,449 adults contacted, 7,268 (86%) agreed to participate in the survey. Participants were from representative socioeconomic and racial/ethnic groups (Table 3) across the United States. The overall monthly participation rate was 83%-87%. Participation rates for men and women were similar.
Of the 7,268 adults surveyed by telephone during 7 surveys (CDC weeks 17-41), 2,337 (32%) said that they had cats in the home, 184 (2.5%) lived in close contact with chickens, and 230(3.2%) answered "yes" when asked "Do you have the fl u?" Of the 230 adults who answered yes to having the fl u, only 49 (21%) reported having received an annual infl uenza vaccine, 68 (30%) reported having fever or abnormal body temperatures, 93 (40%) reported having a cough, and 89 (39%) reported having a sore throat (Table  4). According to CDC infl uenza surveillance reports for weeks 17, 20, and 41 (Table 5)

Discussion
As shown in Table 4, our surveys of 7,268 adult respondents provided nationwide, prepandemic baseline information about household contact with cats (10) (28%-37%) and chickens (1%-4%), factors that may be relevant to the spread of currently circulating strains of avian infl uenza A (H5N1) virus. The data collected in 7 surveys over a 7-month period of low infl uenza activity were consistent with surveillance data gathered and reported by SPN.
More than 80% of persons in the populations and demographic subgroups surveyed nationwide agreed to participate in our study; this rate was similar for all regions of the country. The rate of self-reported illness from "fl u" ranged consistently from 2% to 5% over the 7-month survey period, a time of low infl uenza activity and without reported human illnesses from highly pathogenic avian infl uenza A (H5N1) in the United States. Because only 30% (68/230) of respondents who self-reported the fl u also selfreported fever, it follows that only a very small fraction of all respondents (0.9%, 68/7268) may have met CDC's defi nition of ILI (i.e., fever [>100°F (37.8°C)] and cough or sore throat) (12). Similarly, during the same time frame, the SPN reported outpatient ILI rates of 1.2% and 0.9%, and the other CDC surveillance systems (Table 5) reported only regional and sporadic ILI in most states; moreover, none of the CDC-measured indicators suggested that infl uenza-related illness or death were excessive on the dates our surveys were conducted.
A comparison with CDC surveillance data suggests that the household telephone survey produced plausible, reproducible, and accurate results during a period when the circulation of infl uenza (predominantly infl uenza B virus) in the community was minimal. These results, when interpreted in the context of all other applicable surveillance reports, suggests that a direct telephone survey of adults at home could improve situational awareness of an infl uenza pandemic.Had unexpected trends or inconsistent rates of illness or apparent geographic disparities been identifi ed, an analytic study could have been conducted to suggest possible risk factors or further investigations.
According to the DHHS Pandemic Infl uenza Plan, "Some states are considering the use of systematic phone surveys to supplement SPN data during a pandemic by providing estimates of local cases and affected households. CDC will explore the utility and feasibility of conducting this type of survey on a national level" (2). In a recent national telephone survey of 2,075 persons in Sweden, responses to the question "Did you have the 'fl u' last week?" provided useful public health information regarding ongoing infl uenza disease activity (13). The survey took only 125 working hours to complete and cost approximately €3,250 (US $4,150). On the basis of our results, and assuming appropriate IRB approvals are already in place, we estimate that a new questionnaire could be developed in conjunction with public health offi cials and the telephone survey partners within 1 to 2 days, and the surveys could be conducted over the next 2 days with results delivered essentially immediately to public health offi cials. The direct cost of conducting each of the 2-to 3-day telephone surveys involving 1,200 adults and asking 10 questions was estimated to be $14,000; the 7-survey project in Tables 2-4 had a direct cost of ≈$98,000. In the United States, CDC recently adapted an ongoing national household telephone survey project, the Behavioral Risk Factor Surveillance System (BRFSS), to measure and monitor infl uenza vaccination coverage during the 2004-05 infl uenza season (14). CDC surveyed 26,526 adults during February 1-27, 2005 (14), and reported that ≈6,363 (24%) had been vaccinated. This CDC study also showed that infl uenza vaccination coverage among adults through January of the 2004-05 infl uenza season was greatest among persons >65 years of age (62.7%). In the telephone survey reported here, 21% (49/230) of those adults who self-reported the fl u had re-

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Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 14, No. 1, January 2008  Commercial polling agencies already elicit personal information from the public on an ongoing basis. Recently, as demonstrated by its adaptation of the BRFSS system, CDC was able to obtain information in response to a new public health problem by adding a few questions to an existing telephone survey. Although this adaptation of the survey, data analysis, and reporting infrastructure of the BRFSS appears to have been successful for determining infl uenza health status, it has apparently not yet been translated into a permanent surveillance system or ongoing capability. Moreover, the BRFSS might be overwhelmed in a pandemic emergency and, on very short notice, be forced to use additional telephone surveys that exist in the private and academic sectors. The adaptation of a private opinion survey company's capabilities in partnership with an academic medical center through approved protocols could create a feasible, safe, inexpensive, fl exible, and acceptable way of deriving public health information in emergencies and improving situational awareness.
Our study has several limitations. First, the telephone surveys were conducted only during months with low infl uenza activity in 2006. Second, although 7,268 adults were asked if they had "the fl u," only those who responded affi rmatively (230 adults) were asked further questions about their infl uenza vaccination status and the presence of fever, cough, and sore throat. Biases may have been introduced based on the sequential approach to these questions, because some persons with fever, cough, or sore throat may have been misclassifi ed by answering "No" to have the fl u; additional follow-up questions about these ILI-related symptoms were not asked of all those surveyed. Third, this study had limitations similar to those of CDC's BRFSS: 1) being a land-line telephone-based survey, our study excluded adults in households without telephones and adults who use only cellular telephones; and 2) because the data were self-reported and subject to recall bias, especially for questions that required recall over a longer period, frequency estimates might be less precise for some conditions or behaviors. Fourth, our estimates of the proportion of adults with nondirectory-listed telephone numbers including those who had ILI (12) were based on unmeasured self-reported temperatures (13) rather than on direct observations by healthcare providers, as in the SPN intended for ambulatory populations in healthcare facilities and clinics. Fifth, other illnesses and other viral infections besides infl uenza can cause ILI and can be accompanied by fever, cough, or sore throat. Finally, there was no laboratory confi rmation of infl uenza or ILI in our survey participants.
Nonetheless, we were able to analyze our data in terms of self-reported fever, cough, or sore throat, thereby enabling us to estimate the proportion of respondents who met CDC's defi nition of ILI (12,13). This capability might be useful during an actual pandemic, when it might be more desirable to assess the health status of patients by telephone (15) rather than exposing these and other patients and healthcare workers to the risk for healthcare-associated transmission of respiratory pathogens in clinical settings. Although the SPN's nationwide estimate of ILI, determined using CDC criteria, was similar to our telephone surveybased estimate for the periods of low infl uenza activity in 2006, more data are needed to assess the performance of these methods during seasonal infl uenza peaks and during a pandemic. Others have suggested that sentinel surveillance studies typically underestimate infl uenza in a population; thus, telephone surveys may prove to be an increasingly important component of infl uenza surveillance (13).

Conclusion
Telephone surveys might offer a practical solution to addressing the gaps in knowledge of infl uenza health status that might arise during a pandemic. Further telephone surveys should be performed during the peak infl uenza season to determine whether such an approach to surveillance would be a useful addition to ongoing infl uenza surveillance systems. The usefulness of the telephone survey to gain infl uenza immunization history and current ILI information on all people at risk should also be explored.  Tables 3 and 4.