THE FIVE POINT PERIPHERAL BLOOD SCREEN FOR HANTAVIRUS

THE FIVE POINT PERIPHERAL BLOOD SCREEN FOR HANTAVIRUS CARDIOPULMONARY SYNDROME Glynnis Ingall MD, Ph. D

Hantavirus Cardiopulmonary Syndrome ■ Hantavirus Cardiopulmonary Syndrome (HCPS) is a severe, sometimes fatal, respiratory disease caused by infection with hantavirus ■ Relatively short febrile prodromal period (with chills and myalgia) lasting 3 -5 days. Nonspecific symptoms similar to other viral infections

Rapid Screening for Hantavirus Cardiopulmonary Syndrome (HCPS) Challenges ■ HCPS: Patients may have rapid clinical progression Need for prompt recognition and referral of severe cases to facility where advanced intensive care services are available. ■ Specificity: Patients who are developing HCPS often initially present with clinical features similar to other viral or flu-like illnesses ■ Need for a test that will alert providers to possibility of hantavirus infection ■ Rapid serologic tests for detection of hantavirus antibodies are not yet available ■ Currently it takes 12 -24 hours to perform antibody testing including transport time to laboratory in Albuquerque.

A Rapid Screening Test for HCPS in Rural Areas Desired Features ■ ■ ■ Can be performed with routinely available laboratory equipment Can be performed by non-specialized laboratory technical staff Feasibility to train staff on all shifts and to maintain competency Can be performed without adversely affecting laboratory workflow Provides reliable information that supports clinical decision making.

Development of the 5 Part Hanta Virus Peripheral Blood Screen ■ Koster, F. Foucar, K. Hjelle, B. et al; Rapid Presumptive Diagnosis of Hantavirus Cardiopulmonary Syndrome by Peripheral Blood Smear Review; American Journal of Clinical Pathology; 2001, volume 116; p 665 – 672.

UNM-Five Part Peripheral Blood Screen for HCPS ■ Purpose: To identify a rapid method for presumptive diagnosis of HCPS using peripheral blood counts and smear morphology review. ■ Compared peripheral blood findings of 52 cases of HCPS to 128 control subjects who where sero-negative for hantavirus but clinically mimicked HCPS in prodromal or cardiopulmonary phase. ■ They found an aggregate of five peripheral blood findings which were sensitive and specific enough to allow a presumptive diagnosis of HCPS.

■ Development of the 5 Part Hantavirus Peripheral Blood Screen UNMH implemented a rapid screening tool for the triage of patients with suspected HCPS using the 5 point peripheral blood scoring system. ■ 4 out of 5 cutoff: Sensitivity of 96%, Specificity of 99% - missed no patients requiring intensive care ■ Thrombocytopenia is an early indicator of infection (often seen in prodromal phase) ■ Proposed that the scoring system be used to guide early treatment and patient transport decisions until a rapid, specific, serologic test became widely available.

Five Point Peripheral Blood Scoring for HCPS 1. Thrombocytopenia 2. Left shift in neutrophils 3. Hemo-concentration (Hb/Hct elevated for age and gender) 4. Lack of significant toxic granulation 5. Immunoblasts and plasma cells constituting more than 10% of lymphocytes Note: Value of this scoring system verified with additional decade of use: Dvorscak, L. and Czuchlewski, D. R. “Successful Triage of Suspected Hantavirus Cadiopulmonary Syndrome By Peripheral Blood Smear Review AM J Clin Pathol 2014; 142: 196 -201

Hantavirus Peripheral Blood Screen The five variables used in the scoring system, individually, can be positive in other clinical conditions. Scoring for all five factors and using a cutoff of a score of four or five out of five increases the specificity for HCPS. Note: If HCPS is an ongoing clinical consideration and hantavirus score is equivocal, then serial testing could be offered (8 -12 hour intervals).

HCPS - Platelets In about 80% of individuals with HCPS, the platelet count is below 150, 000. A dramatic fall in the platelet count may herald a transition from the prodromal to the pulmonary edema phase of the illness.

Platelets ■ Note: Thrombocytopenia is not uncommon in viral illness therefore this factor alone is not specific for HCPS ■ Thrombocytopenia can be seen in other infections (sepsis, plague, tularemia, borreliosis, Rocky Mountain spotted fever, and parvovirus) as well as in other noninfectious conditions

HCPS-Elevated Hb/Hct for age and gender Hemoconcentration: A rise in the hematocrit may indicate a fluid shift from the patient's circulation into the lungs in patients with HCPS. Note: When evaluating the significance of the hemoconcentration, the clinician should be aware of other pre-existing causes of erythrocytosis such as chronic pulmonary disease.

HCPS – Left Shift in Neutrophil Series and Lack of Significant Toxic Granulation In HCPS, the white blood cell count tends to be raised with a left shift. However, toxic granulation is negligible or absent. Note: In bacterial infections with elevated white count and left shift, toxic changes are prominent.

HCPS- Immunoblasts/Plasma cells Greater than 10% of Lymphocytes Immunoblasts/plasma cells are frequently present, usually at the time of onset of pulmonary edema. (Numbers tend to decline during convalescence) Notes: Immunoblasts alone are not specific for HCPS. They are seen in peripheral blood smears in small numbers as the result of transient immune response of diverse etiologies.

Hantavirus Peripheral Blood Screen Scoring System 1. Hgb/Hct elevated for gender/age Yes No 2. Left shift of granulocytic series Yes No 3. Absence of toxic changes Yes No 4. Thrombocytopenia Yes No 5. Immunoblasts & Plasma Cells > 10% of lymphocytes Yes No

4 -5 out of 5 Criteria Based upon the UNMH experience, the positive predictive value is 90% for cases fulfilling 4 of 5 criteria and greater than 90% for cases meeting 5 of 5 criteria when the patient has other clinical features suggestive of Hantavirus cardiopulmonary syndrome. Serum specimen for serologic confirmation is indicated.

3 out of 5 Criteria Blood features are non-diagnostic at this time for Hantavirus cardiopulmonary syndrome. If an early Hantavirus infection is still a clinical consideration, repeat peripheral blood screening in 12 hours may be of value.

1 -2 out of 5 Criteria Blood features are non-diagnostic at this time. Repeat evaluation is recommended if clinically warranted.

Limitations of Five Point Peripheral Blood Screen for HCPS ■ For the UNM study, the estimates of sensitivity and specificity were determined on a patient population with high pre-test probability of HCPS (Most patients in region with suspected HCPS are transferred to UNMH for advanced care). ■ The estimates of Positive Predictive Value of this test would be substantially lower in parts of the country where hantavirus infection prevalence is low. Therefore, the screen would not be appropriate to perform in non-endemic areas. ■ Will the positive predictive value of the test be as high in the community setting where patients may be seeking care at an earlier stage of hantavirus infection or may have other pre-existing clinical conditions that may affect scoring system (cirrhosis, COPD etc. )?

Limitations: Continued Hemato-pathologist vs. Technologist Scoring For the UNM study, the hantavirus peripheral blood scores were determined by hemato-pathologists. The authors of the original paper were concerned as to whether this test could be performed by rural hospital technologists. Note: Experience at TMC has shown that laboratory technologists (both 2 yr and 4 yr degreed) on all shifts and with varying years of work experience can perform these screens accurately and consistently after appropriate training.

Limitations: Continued ■ Hantavirus testing not performed when indicated Hantavirus peripheral blood screening may not be performed, even if available, if providers do not consider the possibility of hantavirus infection in patients presenting with flu-like febrile illness. This may be an issue with contract providers who were trained or primarily practice in non-endemic areas. ■ Reflex hanta virus screening for thrombocytopenia In order identify patients with possible HCPS, consider adding a reflex hantavirus screen for ED or urgent care patients who present with thrombocytopenia and respiratory illness. Note: At TMC, Four out of the five cases with high peripheral blood scores and Ig. M positive serology for hantavirus were discovered first by the lab due to reflex testing for thrombocytopenia.

Limitations ■ Presumptive Diagnosis of HCPS: Scoring system is a screening test for patients who may have hantavirus cardiopulmonary syndrome. It is a presumptive diagnosis supported by appropriate clinical and history findings. Confounding chronic clinical conditions may need to be considered when interpreting the significance of a given score. ■ Not a test for exposure to hantavirus: Scoring system can not determine exposure to hantavirus or distinguish milder forms of hantavirus infection from other causes of viral illness. ■ Collect serum sample: Collect a sample for serologic confirmation when performing a hantavirus peripheral blood screen. Positive Ig. M antibodies for hantavirus suggests acute infection.

Summary ■ Currently, the hantavirus 5 part peripheral blood score is the only rapid screening test for patients who may be developing hantavirus cardio-pulmonary syndrome. ■ Implementation of this test at clinical labs in endemic area is feasible. No specialized equipment or staffing are required ■ Consider offering the test both as a provider-ordered and as a reflex for patients presenting to the ED or urgent care with thrombocytopenia. ■ For case follow-up: Contact your state department of health and obtain a serology (serum) specimen for hantavirus Ig. G and Ig. M testing. ■ For information about clinical management of hantavirus cardio-pulmonary syndrome, call University of New Mexico Physician Access Line at: 505 272 -2000.