Influenza in ICD10

This page contains an ICD10 Coding Guideline for ICD10 collection. See ICD10 coding guidelines for similar pages.

Identifying the Presence of Influenza

• It's not always simple. The reason is that the value of lab tests in helping us figure out whether a person has influenza depends on:
  • a) how long after onset of symptoms the test was done
  • b) which test was done,
  • c) whether the sample was upper or lower respiratory, and
  • d) when, relative to that year's flu season the test was done.

• Based on this, ICD-10 coding for identification of influenza will be as follows:
  • Look at this WRHA website to identify whether we are in flu season

During flu season

a person will be considered to have influenza if either of the following is true:

• i) 'ANY' type of test done for influenza was positive, or
• ii) the patient was believed, by the medical team, to have influenza and is given a full course of treatment (which could possibly have concluded after leaving the hospital, or they could have died before completing the full course).
• NOTE
  • a person can be diagnosed as having influenza even if no test was sent, OR EVEN when tests sent were negative if they meet criterion "(ii)" above.
  • For criteria (i) above, during flu season, "any lab test" means preliminary Cadham result or final Cadham result, or even the rapid swab done by the individual hospital labs.

Off flu season

• Off flu season is defined as: before there is any reported flu in the province, and after the flu season has been declared to be over.
• Off flu season, a person can ONLY be diagnosed as having influenza only if the FINAL CADHAM result was positive.
• In the absence of such a final Cadham result, clinical suspicion, treatment for flu, and positive rapid tests will be considered as NOT INFLUENZA.

What is a FULL COURSE of Antiviral Treatment?

• Oseltamivir (Tamiflu) or another anti-Flu agent is given for 5 days for mild disease.
• WHO and CDC however, recommend that in severe cases (including all cases requiring mechanical ventilation) the drug should be continued until the infection is resolved or there is satisfactory clinical improvement.
• Thus, sometimes this will be a judgement call on the part of the data collector.

type of influenza tests

As of January 2018 there are 3 "flavors" of influenza tests being done in the WRHA:

1. some individual hospital labs run a test locally, done only on swabs (not body fluids)
2. Cadham does a “Preliminary” test
3. Cadham does the “FINAL” testing, which they will run on either nasal swabs or body fluids

Difference between WRHA infection control & our ICD10 Influenza definition

• The way this definition differs from that of the WRHA is primarily that -- if a test was done -- they consider a person negative (influenza ruled out) if the FINAL Cadham result is negative, while during flu season we consider that person to be +influenza if the medical team thought they had influenza and gave the person a full course of antiviral drug.
• We are aware that neither of these approaches are THE TRUTH. The WRHA definition almost certainly slightly under counts cases, while our ICD10 definition listed above almost certainly slightly over counts cases.

Coding other infections caused by influenza virus

Use and see Influenza virus NOS -- should almost never be used#Coding other infections caused by influenza virus.

ICD10 Diagnosis codes for Influenza

There are 4 influenza-related codes we're using in ICD10.

• 3 code are for actual disease due to influenza:
  • Influenza pneumonia
  • Influenza without pneumonia but with other respiratory manifestations
  • Influenza with nonrespiratory manifestations
• The 4th has a long & weird name: Influenza virus NOS -- should almost never be used (see more info in that article)
  • See: Wikipedia for types of virus included

Alternate ICD10s to consider coding instead or in addition

• Haemophilus influenzae (H. flu) (this is not an influenza pathogen)
• Parainfluenza virus (this is not influenza an pathogen)