Z77.121 Contact with and (suspected) exposure to harmful algae and algae toxins

Billable ICD-10-CM code, FY2026. Exempt from present-on-admission (POA) reporting.

Applicable to

• Contact with and (suspected) exposure to (harmful) algae bloom NOS
• Contact with and (suspected) exposure to blue-green algae bloom
• Contact with and (suspected) exposure to brown tide
• Contact with and (suspected) exposure to cyanobacteria bloom
• Contact with and (suspected) exposure to Florida red tide
• Contact with and (suspected) exposure to pfiesteria piscicida
• Contact with and (suspected) exposure to red tide

Applies from Z77 Other contact with and (suspected) exposures hazardous to health

Includes

• contact with and (suspected) exposures to potential hazards to health

Excludes2 (not included here)

• contact with and (suspected) exposure to communicable diseases (Z20.-)
• exposure to (parental) (environmental) tobacco smoke in the perinatal period (P96.81)
• newborn affected by noxious substances transmitted via placenta or breast milk (P04.-)
• occupational exposure to risk factors (Z57.-)
• retained foreign body (Z18.-)
• retained foreign body fully removed (Z87.821)
• toxic effects of substances chiefly nonmedicinal as to source (T51-T65)

MS-DRG index

Defines the logic of DRG(s) 951 in MDC 23.

Approximate ICD-9-CM (GEMs)

• V87.32 Contact with and (suspected) exposure to algae bloom (approximate)

Medicare Code Edits (MCE v43.1 (April 2026))

• Unacceptable principal diagnosis: These codes describe a circumstance which influences care but is not a current illness or injury, or capture only an underlying condition, and are unacceptable as principal diagnosis.

Code annotations containing back-references to Z77.121

Back-references to Z77.12

• Type 1 Excludes: Z92.3 Personal history of irradiation ("exposure to radiation in the physical environment (Z77.12)")

Back-references to Z77.1

• Type 2 Excludes: Z59.1 Inadequate housing ("problems related to the natural and physical environment (Z77.1-)")
• Type 2 Excludes: Z91 Personal risk factors, not elsewhere classified ("exposure to pollution and other problems related to physical environment (Z77.1-)")

Back-references to Z77

• Type 2 Excludes: P04 Newborn affected by noxious substances transmitted via placenta or breast milk ("newborn in contact with and (suspected) exposures hazardous to health not transmitted via placenta or breast milk (Z77.-)")
• Type 1 Excludes: Z03 Encounter for medical observation for suspected diseases and conditions ruled out ("contact with and (suspected) exposures hazardous to health (Z77.-)")
• Type 1 Excludes: Z13.88 Encounter for screening for disorder due to exposure to contaminants ("those exposed to contaminants without suspected disorders (Z57.-, Z77.-)")
• Type 2 Excludes: Z91 Personal risk factors, not elsewhere classified ("contact with and (suspected) exposures hazardous to health (Z77.-)")

Diagnosis Index entries for Z77.121

• Contact (with) › algae and algae toxins
• Contact (with) › algae bloom
• Contact (with) › blue-green algae bloom
• Contact (with) › brown tide
• Contact (with) › cyanobacteria bloom
• Contact (with) › pfiesteria piscicida
• Contact (with) › red tide (Florida)
• Exposure (to) › algae and algae toxins
• Exposure (to) › algae bloom
• Exposure (to) › blue-green algae bloom
• Exposure (to) › brown tide
• Exposure (to) › cyanobacteria bloom
• Exposure (to) › pfiesteria piscicida
• Exposure (to) › red tide (Florida)

Nearby codes

• Z77.111 Contact with and (suspected) exposure to water pollution
• Z77.112 Contact with and (suspected) exposure to soil pollution
• Z77.118 Contact with and (suspected) exposure to other environmental pollution
• Z77.12 Contact with and (suspected) exposure to hazards in the physical environment
• Z77.120 Contact with and (suspected) exposure to mold (toxic)
• Z77.121 Contact with and (suspected) exposure to harmful algae and algae toxins (this code)
• Z77.122 Contact with and (suspected) exposure to noise
• Z77.123 Contact with and (suspected) exposure to radon and other naturally occurring radiation
• Z77.128 Contact with and (suspected) exposure to other hazards in the physical environment
• Z77.2 Contact with and (suspected) exposure to other hazardous substances
• Z77.21 Contact with and (suspected) exposure to potentially hazardous body fluids