. 2021 May 20;224(12):2035–2042. doi: 10.1093/infdis/jiab273

Table 1.

Rationale and Descriptions of Influenza Clinical Testing Scenarios 1–5 Among Acute Respiratory Infection (ARI) Patients

Two-by-Two Tables of Scenarios 1–5, With 25% Overall Reduction in Testing		Description of Clinical Testing Scenarios	Rationale
Scenario 1: Influenza Negative Patients Tested Less Than Others		Less testing in patients without influenza, independent of vaccination (targeted cells are b and d) by increasing C’p_b and C’p_d from baseline by 5%, 10%, and 15% (scenarios 1a–c)*. The proportionate reductions in C’p_b:p_b, C’p_c:p_c, and C’p_d:p_d can be computed by: $C^{'} p_{a} : p_{a} = C^{'} p_{c} : p_{c} = [1 - ((p_{b} x v) + (p_{d} x v))] / (p_{a} + p_{c})$ Where v = 0.05, 0.10, or 0.15	Clinicians may be less likely to test ARI patients who are less likely to have influenza and/or more likely to test patients with more severe symptoms (influenza causes more severe symptoms on average than other etiologies of ARI [19, 20]).
Vaccinated, influenza positive case Cell a	Vaccinated, influenza negative control Cell b
Unvaccinated, influenza positive case Cell c	Unvaccinated, influenza negative control Cell d
Scenario 2: Vaccinated Patients Tested Less Than Others		Less testing in vaccinated patients, independent of influenza status by increasing C’p_a and C’p_b from baseline by 10%, 25%, and 50% (targeted cells a and b, scenarios 2a–c)* The proportionate reductions in C’p_b:p_b, C’p_c:p_c, and C’p_d:p_d can be computed by: $C^{'} p_{c} : p_{c} = C^{'} p_{d} : p_{d} = [1 - ((p_{a} x v) + (p_{b} x v))] / (p_{c} + p_{d})$ Where v = 0.1, 0.25, or 0.5	Clinicians may ask about influenza vaccination, believe influenza infection is more likely in unvaccinated patients, and therefore target influenza testing for unvaccinated patients. Factors related to healthcare-seeking behavior could also result in this pattern of testing; for example, patients with primary care physicians may be more likely to be vaccinated and may be less likely to undergo influenza testing for an ARI because clinicians treating the ARI may opt for less testing for patients who have established providers for close follow-up.
Vaccinated, influenza positive case Cell a	Vaccinated, influenza negative control Cell b
Unvaccinated, influenza positive case Cell c	Unvaccinated, influenza negative control Cell d
Scenario 3: Vaccinated Influenza Positive Patients Tested Less Than Others		Less testing in vaccinated patients with influenza by increasing C’p_a by 10%, 25%, and 50% from baseline (targeted cell a, scenarios 3a–c)* C’p_a = pa (1+i) The proportionate reductions in C’p_b:p_b, C’p_c:p_c, and C’p_d:p_d can be computed by: $C^{'} p_{b} : p_{b} = C^{'} p_{c} : p_{c} = C^{'} p_{d} : p_{d} = (1 - p_{a} x v) / (p_{b} + p_{c} + p_{d})$ Where v = 0.1, 0.25, and 0.50	Clinicians may be less likely to test ARI patients who are vaccinated and likely to have influenza if influenza vaccination attenuates the severity of ARI symptoms [21, 22], and clinicians preferentially test patients with higher severity.
Vaccinated, influenza positive case Cell a	Vaccinated, influenza negative control Cell b
Unvaccinated, influenza positive case Cell c	Unvaccinated, influenza negative control Cell d
Scenario 4: Vaccinated Influenza Negative Patients Tested Less Than Others		Less testing in vaccinated patients without influenza by increasing C’p_b by 10%, 25%, and 50% (targeted cell b, scenarios 4a–c) from baseline*. The proportionate reductions in C’p_b:p_b, C’p_c:p_c, and C’p_d:p_d can be computed by: $C^{'} p_{a} : p_{a} = C^{'} p_{c} : p_{c} = C^{'} p_{d} : p_{d} = (1 - p_{b} x v) / (p_{a} + p_{c} + p_{d})]$ Where v = 0.1, 0.25, or 0.5	In this situation, clinicians may be less likely to test vaccinated patients with milder symptoms less indicative of influenza (and more indicative of other respiratory viruses).
Vaccinated, influenza positive case Cell a	Vaccinated, influenza negative control Cell b
Unvaccinated, influenza positive case Cell c	Unvaccinated, influenza negative control Cell d
Scenario 5: Unvaccinated Influenza Positive Patients Tested More Than Others		More testing (less nontesting) in unvaccinated patients with influenza by decreasing C’p_c by 10%, 25%, and 50% (targeted cell c, scenarios 5a–c) from baseline. The proportionate changes in C’p_b:p_b, C’p_c:p_c, and C’p_d:p_d can be computed by: $C^{'} p_{a} : p_{a} = C^{'} p_{b} : p_{b} = C^{'} p_{d} : p_{d} = (1 - p_{c} x v) / (p_{a} + p_{b} + p_{d})]$* Where v = −0.1, −0.25, or −0.5	Clinicians may be more likely to suspect influenza and test ARI patients who are unvaccinated and more likely to have influenza.
Vaccinated, influenza positive case Cell a	Vaccinated, influenza negative control Cell b
Unvaccinated, influenza positive case Cell c	Unvaccinated, influenza negative control Cell d

^aBlack arrows represent the targeted reduction in testing.

*With accompanying increases or decreases in testing among other patients to maintain overall proportion nontested of 25%.

NOTE: C’pa, C’pb, C’pc, and C’pd: denote the proportion of nontested ARI patients that are in cells a, b, c, and d, respectively; C’ denotes proportion untested overall; number nontested overall = N*C’; p_a, p_b, p_c, p_d denote the proportion of total ARI patients in each cell.