Validity of clinical case definitions for influenza surveillance among hospitalized patients: results from a rural community in North India

Abstract

Objective: Clinical case definitions used for influenza surveillance among hospitalized patients vary and need systematic evaluation. Design, setting and sample: During July 2009–August 2011, we collected clinical data and specimens (nasal and throat swabs) from rural patients hospitalized for acute medical illnesses. Specimens were tested by rRT‐PCR for influenza viruses. Main outcome measures: Case definitions evaluated the following: influenza‐like illness (ILI: measured fever plus cough or sore throat); severe acute respiratory illness (SARI: ILI with difficulty breathing in ≥5 years, Integrated Management of Childhood Illness–defined pneumonia or severe pneumonia, or physician diagnosed lower respiratory infection in <5 years); acute respiratory infection (ARI: ≥1 of cough, nasal discharge, difficulty breathing or sore throat); febrile acute respiratory illness (FARI: fever plus either cough, sore throat, runny nose, difficulty breathing, or earache). Variants that included “reported fever” and additional sign–symptom combinations were also evaluated. Results: We enrolled 1043 hospitalized patients, including 257 children <5 years of age (range 1 day–86 years). Seventy‐four patients tested influenza virus positive (including 28 A(H1N1)pdm09). Sensitivity(95% CI) and specificity (95% CI) for influenza infection were 78% (67–87) and 60% (57–63) for ILI (measured/reported fever); 37% (26–49) and 78% (75–80) for SARI (measured/reported fever); 82% (72–90) and 57% (54–60) for FARI (measured/reported fever); 88% (78–94) and 45% (42–49) for ARI; and 74% (63–84) and 61% (58–64) for measured/reported fever plus cough. Case definitions including only measured fever had lower sensitivity. Conclusion: ILI and FARI with measured/reported fever provided good balance between sensitivity and specificity among hospitalized patients. The simpler case definition of measured/reported fever plus cough is suited for field surveillance.

Performance of case definitions used for influenza surveillance among hospitalized patients in a rural area of India

“…27,28 The sensitivities (69-70%) and specificities (43-53%) recorded for the case definition for influenza-like illness in the present study are similar to the corresponding sensitivities (73-78%) and specificities (49-65%) recently reported in northern India, in a study that used the same broad enrolment criteria. 27 However, the same case definition appeared less sensitive but more specific when investigated in Kenya, in a study confined to patients with acute respiratory illness. 28 In the present study, 13% of the hospitalized patients aged < 5 years and 22% of those aged ≥ 5 years were found PCR-positive for influenza viruses.…”

“…Very few published studies have evaluated influenza case definitions among hospitalized patients with a similarly broad spectrum of acute illness, including non-respiratory illness. 17,27 Although WHO's case definition for severe acute respiratory illness has frequently been used to screen for influenza among hospitalized patients, our findings indicate that the use of this case definition (both among hospitalized children aged < 5 years and among older hospitalized patients) results in a low detection of influenza cases, although those meeting the case definition are likely to harbour an influenza virus. Similarly low sensitivities have been recorded for this case definition in other studies, at least among patients aged ≥ 5 years.…”

“…Similarly low sensitivities have been recorded for this case definition in other studies, at least among patients aged ≥ 5 years. 27 Since, in the present study, patients were checked for shortness of breath, difficulty breathing and tachypnea by trained study physicians, the low numbers of patients with these problems were unlikely to be attributable to under-detection. These problems may have been encountered relatively rarely in the present study because concerns raised by the influenza pandemic that occurred during the study period (i.e.…”

Contribution of influenza to acute exacerbations of chronic obstructive pulmonary disease in Kashmir, India, 2010–2012

“…However, only 8% of patients in our study reported receiving influenza vaccine, consistent with limited data on uptake in other high‐risk groups in India . Our findings, along with emerging data on influenza virus circulation and influenza‐associated hospitalization incidence in other parts of India, suggest that influenza is a substantial contributor to severe respiratory illness in India and that recommendations for influenza vaccination in certain high‐risk groups may be warranted.…”

Incidence of influenza-associated hospitalization in rural communities in western and northern India, 2010–2012: A multi-site population-based study

“…In a previous analysis from the same study, we showed that the sensitivity of original WHO ILI case definition was 78% in Ballabgarh and 87% in Vadu and we would accordingly underestimated the burden had we used the ILI case definition to estimate influenza-associated hospitalization incidence in our study. 17,18 The observed differences in influenza-associated hospitalization incidences between sites in our study could have been partially explained by differences in influenza circulation and transmission. Data from influenza sentinel surveillance conducted at Delhi, the closest city to Ballabgarh, and Pune, the closest city to Vadu, consistently indicated higher levels of influenza virus detection during our study period suggesting that there were true differences in influenza virus circulation and transmission between northern and western India during this time.…”