Coding for Zika: Unraveling the Threat of a Silent Predator

Coding for Zika
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When we consider treacherous animals, our thoughts may drift to lions, bears, and sharks. Yet, the true menace is a far less conspicuous creature: the mosquito. This seemingly harmless insect can spread many deadly diseases, including Zika, dengue fever, yellow fever, and West Nile virus. In this article, our focus is on the Zika virus, exploring its means of transmission, presenting symptoms, diagnostic methods, and available treatments. Furthermore, we shed light on medical coding for Zika, providing nine detailed examples to simplify the accurate assignment of ICD-10-CM codes in accordance with established guidelines and conventions.

Zika, also known as Zika virus disease, Zika virus fever, or Zika virus infection, is an infectious disease caused by the Zika virus, primarily transmitted by infected Aedes species mosquitoes. These mosquitoes are active throughout the day, posing a continuous threat. Moreover, Zika can be transmitted from a pregnant woman to her fetus, through sexual contact, and possibly via blood transfusion. This virus infection is particularly alarming for at-risk populations and can significantly impact pregnant women and their fetuses. Presently, no vaccine exists for Zika prevention nor a specific treatment for the disease.

The History of Zika

The first case of the Zika virus was identified in 2007, with a significant outbreak occurring in Brazil in 2015. This outbreak led to reports of Guillain-Barre syndrome and adverse pregnancy outcomes, such as congenital disabilities, preterm births, and spontaneous abortions. Subsequently, annual alerts regarding Zika outbreaks have become customary. In February 2024, several countries and territories in the Region of the Americas reported a significant increase in locally transmitted Zika cases, emphasizing the urgent need for intensified efforts to control the primary vector of disease transmission, the Aedes aegypti mosquito. 

Understanding the Symptoms

The symptoms of Zika virus infection can vary widely, with some individuals displaying no symptoms at all while others experience mild symptoms lasting 2 to 7 days. Common manifestations include fever, rash, headache, joint pain, conjunctivitis, and muscle pain. These symptoms closely resemble those of other mosquito-borne viruses like dengue and chikungunya. Given the asymptomatic nature of many cases, individuals may remain unaware of their infection. While Zika rarely proves fatal, it poses substantial risks to pregnant women and their fetuses. 

Diagnostic Approaches

Diagnosing Zika typically involves a thorough assessment of the patient’s recent travel history and symptoms, followed by blood or urine tests to confirm the presence of the virus. Molecular or serological tests are recommended for symptomatic individuals with a history of travel to regions experiencing Zika outbreaks. In pregnant women, a molecular test is preferred, especially if Zika-related abnormalities are detected during ultrasound examinations or if adverse pregnancy outcomes occur. Additionally, there’s a risk of sexual transmission, necessitating testing for individuals with potential exposure.

Treatment and Complications

Regrettably, no specific treatment or vaccine is available for Zika virus infection. Nevertheless, several investigational vaccines are under development. Management typically involves rest, hydration, and pain relief with medications like acetaminophen (Tylenol). However, Zika’s potential complications are a cause for serious concern due to associations with Guillain-Barre syndrome, neuropathy, myelitis, and, most alarmingly, congenital abnormalities such as microcephaly in infants born to infected mothers.

Prevention of Zika

Preventing Zika virus disease primarily involves reducing exposure to mosquitoes, mainly the Aedes species, which transmits the virus. Precautions include using insect repellents containing DEET, wearing long-sleeved clothing, and using screens on windows and doors to prevent mosquitoes from entering living spaces. Additionally, eliminating standing water where mosquitoes breed, such as in flower pots, buckets, and gutters, is crucial. Travelers to areas with Zika outbreaks should take extra safeguards, such as staying in accommodations with air conditioning or screened windows and using mosquito nets while sleeping. Pregnant women, in particular, should avoid travel to areas with active Zika transmission to reduce the risk of congenital disabilities associated with the virus. 

Coding for Zika Virus Disease in ICD-10-CM

Coding for Zika virus disease varies according to its distinct clinical presentations and implications, particularly for pregnancy. Acquired Zika infections are classified under A92.5, whereas congenital cases are coded as P35.4. Correct coding is based on the ICD-10-CM Official Guidelines for Coding and Reporting, primarily when documenting suspected or confirmed cases.

The Zika-related guidelines, which complement the coding conventions and instructions, are as follows:

  • Code only a confirmed diagnosis of Zika virus (A92.5, Zika virus disease) as documented by the provider.
  • For hospital inpatient coding, confirmation of Zika does not require documentation of the type of test performed. Instead, the provider’s diagnostic statement that the condition is confirmed is sufficient. This rule applies to any stated mode of transmission. 
  • If the provider documents “suspected,” “possible,” or “probable” Zika, do not assign A92.5. Instead, assign a code(s) explaining the reason for the encounter (such as fever, rash, or joint pain) or Z20.821, Contact with and (suspected) exposure to Zika virus.
  • For inpatient coding only: If the diagnosis documented at the time of discharge is qualified as “probable,” “suspected,” “likely,” “questionable,” “possible,” or “still to be ruled out,” “compatible with,” “consistent with,” or other similar terms indicating uncertainty, code the condition as if it existed or was established. The basis for these guidelines is the diagnostic workup, arrangements for further workup or observation, and initial therapeutic approach that corresponds most closely with the established diagnosis. 

To illustrate correct coding, we provide a series of coding examples and detailed rationales to demonstrate appropriate ICD-10-CM coding for Zika virus disease. 

Zika Coding Examples

Solve the following coding exercises, and then review the answers and rationales in the next section.

1. A patient presents to her physician with headache, fever, conjunctivitis bilaterally, and arthralgia in the hands and feet. The patient is tested and diagnosed with Zika virus disease.

2. A pregnant woman diagnosed with Zika virus transmitted the infection to her fetus in utero, which manifested into microcephaly. Code for the baby’s record.

3. A 37-year-old male presents with a low-grade fever, rash, and acute conjunctivitis bilaterally. The patient has just returned from a trip to Brazil. After examination and testing for the Zika virus, the patient is diagnosed with suspected Zika. 

4. A patient is seen due to concerns after being exposed to the Zika virus. She currently has no symptoms, and test results are unknown. 

5. A pregnant patient in her second trimester has tested positive for Zika virus fever.

6. A pregnant woman is seen today for prenatal care. She is in her 28th week of gestation, has a confirmed diagnosis of Zika virus infection, and a previously diagnosed case of suspected fetal anomalies. Code for the mother’s record.

7. A woman in her 8th week of pregnancy is seen by the obstetrician for a prenatal visit. She reports that her sexual partner has been diagnosed with Zika virus, but she has no symptoms of the virus. 

8. The patient has been diagnosed with Zika virus fever. Before prescribing methacycline, a tetracycline antibiotic, an antibiotic sensitivity test is performed, and the patient is found to be resistant to the antibiotic. 

9. A patient was diagnosed with Guillian-Barre Syndrome, which is linked to a recent Zika virus infection. The patient no longer has Zika. 

Answers and Rationales

1. Answer:

  • A92.5, Zika virus disease

Rationale: This is an acquired case of Zika virus disease, which has been confirmed. There is no need to code for the symptoms, as they are integral to Zika, and the classification does not instruct the coder to do otherwise. Under A92.5 (Zika virus disease), there is a non-exhaustive list of inclusion terms, including Zika virus fever, Zika virus infection, and Zika NOS.   

2. Answer:

  • P35.4, Congenital Zika virus disease
  • Q02, Microcephaly

Rationale: The infant was born with Zika, which resulted in a congenital complication – microcephaly (smaller than normal head size). Congenital Zika virus disease is coded as P35.4. At P35.4, a “Use additional” note tells us to code to identify manifestations of congenital Zika virus disease, which is microcephaly. According to the note, microcephaly is reported with Q02 and is sequenced after P35.4. Codes from this chapter are for use on newborn records only and can never be used on maternal records. Looking at Q02, Microcephaly, in the Tabular, a “Code First” note instructs us to code for congenital Zika virus disease, if applicable. 

3. Answer:

  • R50.9, Fever, unspecified
  • R21, Rash, and other nonspecific skin eruption
  • H10.33, Unspecified acute conjunctivitis, bilateral

Rationale: Fever, rash, and conjunctivitis are common symptoms of the Zika virus and should not be coded when a confirmed diagnosis of Zika is documented. In this case, however, the diagnosis is “suspected” Zika, so in outpatient coding, we must code for the symptoms to explain the encounter, as specified by the coding guidelines. Fever (R50.9) and acute conjunctivitis (H10.33) are reported with “unspecified” codes, as the particular types are not documented. Furthermore, as documented, a nonspecific type of skin rash is assigned to R21. 

4. Answer:

  • Z20.821, Contact with and (suspected) exposure to Zika virus

Rationale: The patient is asymptomatic but is being screened for Zika due to (suspected) exposure and being at risk of acquiring and possibly further spreading the disease to others. When there are no symptoms or confirmation of Zika, assign Z20.821, Contact with and (suspected) exposure to Zika virus. 

5. Answer:

  • O98.512, Other viral diseases complicating pregnancy, second trimester
  • A92.5, Zika virus disease

Rationale: A confirmed diagnosis of Zika virus fever is reported, which is complicating the woman’s pregnancy. A confirmed Zika diagnosis is reported with A92.5. An “Excludes2” note instructs the coder to assign O98.- for infectious and parasitic diseases complicating pregnancy, childbirth, and the puerperium. The patient is pregnant and in her second trimester, so we must assign O98.512, Other viral diseases complicating pregnancy, second trimester. A “Use additional” note at O98 states that a code from Chapter 1 must be reported to identify the specific infection or parasitic disease. (A92.5, Zika virus disease) This note also explains the sequencing of the two codes; O98.512 is sequenced first, followed by A92.5. Finally, a note tells us that codes from this chapter are for use only on maternal records, never on newborn records.  

6. Answer:

  • O35.3XX0, Maternal care for (suspected) damage to fetus from viral disease in mother, not applicable or unspecified
  • O98.513, Other viral diseases complicating pregnancy, third trimester
  • A92.5, Zika virus disease
  • Z3A.28, 28 weeks gestation of pregnancy

Rationale: The pregnant patient has been diagnosed with Zika virus infection and suspected fetal anomalies. Again, the code for a confirmed diagnosis of Zika is A92.5. An “Excludes2” note in Chapter 1 indicates that infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium must be coded to O98.-. Since the patient is 28 weeks pregnant and in her third trimester, the coder must assign O98.513 (Other viral diseases complicating pregnancy, third trimester). Under O98, a “Use additional” note tells us to assign a code from Chapter 1 to identify specific infectious or parasitic disease, which is A92.5. Another instructional note tells the coder to use an additional code, if applicable, from category Z3A, Weeks of gestation, to identify the specific week of the pregnancy, if known. For 28 weeks gestation of pregnancy, we need to assign Z3A.28. The “Code First” note at Z3A tells the coder to sequence the obstetric condition or encounter for delivery, which, in this case, is O35.3XX0. These codes must be used only on the mother’s record.

7. Answer:

  • Z34.91, Encounter for supervision of normal pregnancy, unspecified, first trimester
  • Z20.821, Contact with and (suspected) exposure to Zika virus

Rationale: The patient presents for a regular prenatal visit and is in her 8th week of pregnancy or first trimester. The documentation does not specify first pregnancy, normal pregnancy, or other types of pregnancy, so we must assign an “unspecified” code, Z34.91 (Encounter for supervision of normal pregnancy, unspecified, first trimester). A code must also be assigned from category Z20.- to report her exposure to the Zika virus and potential risk. This code, Z20.821 (Contact with and (suspected) exposure to Zika virus), is used when there are no symptoms and to report testing for the infection. Furthermore, if the patient is diagnosed with Zika, it must be coded and sequenced after the Z20.- code. In this case, however, nothing has been documented as to a Zika diagnosis.

8. Answer:

  • A92.5, Zika virus disease
  • Z16.29, Resistance to other single specified antibiotic

Rationale: Zika virus fever, an inclusion term listed under A92.5, Zika virus disease, is assigned for the confirmed diagnosis. A “Use additional” note indicates that a code from Z16.- must be assigned to identify resistance to antimicrobial drugs. The documentation states the patient is resistant to methacycline, a tetracycline antibiotic. Since there is no specific code for this type of drug, we must code to “other” and assign Z16.29 (Resistance to other single specified antibiotic). Inclusion terms listed under Z16.29 are Resistance to aminoglycosides, Resistance to macrolides, Resistance to sulfonamides, and Resistance to tetracyclines. There is a “Code First” note at Z16 to sequence the code for the infection before Z16.29. 

9. Answer:

  • G61.0, Guillain-Barré syndrome
  • B94.8, Sequelae of other specified infectious and parasitic diseases

Rationale: Guillain-Barre syndrome (GBS) developed as a sequela, or late effect, of Zika.The code for Guillain-Barre syndrome is G61.0, with inclusion terms listed as Acute (post-) infective polyneuritis and Miller-Fisher Syndrome. An “Excludes2” note at G00-G99 tells the coder to assign a code from A00-B99 for certain infectious and parasitic diseases. Since Zika is no longer present, we cannot code A92.5. However, since GBS is a sequela of Zika, B94.8, Sequelae of other specified infectious and parasitic diseases, must be assigned. A “Code First” note at B90-B94 also instructs the coder to sequence the code for the condition resulting from the infectious or parasitic disease before B94.8.


In the world of infectious diseases, Zika has the potential to cause widespread devastation, especially among vulnerable populations. Effective management requires various approaches: prevention, diagnosis, and supportive care. Furthermore, accurate medical coding is vital to capturing the distinctions of Zika’s impact on healthcare systems. By understanding and implementing the coding guidelines and conventions related to acquired and congenital Zika virus disease and its complications, coders can ensure timely and appropriate reimbursement and improve patient safety.   

Coding for Zika
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I submitted this article to BC Advantage/ for their publication. It is reprinted here with their permission.



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