{
  "slug": "lyme-disease-tick-bite",
  "question": "What are the odds of getting Lyme disease from a tick bite?",
  "category": "health",
  "no_reliable_estimate": false,
  "perceived": {
    "description": "Lyme disease occupies a peculiar niche in risk perception: in the northeastern United States, it is a near-universal worry during tick season, with parents, hikers, and gardeners treating every embedded tick as a medical emergency. In non-endemic regions — the Mountain West, most of the South, the Pacific Northwest — the same tick bite barely registers. No rigorous national poll isolates \"fear of Lyme disease from a single tick bite\" as a standalone question, so the perceived estimate here is editorial intuition calibrated by regional conversation patterns rather than survey data.\n",
    "rough_estimate": "endemic-area residents often guess 30–50% per bite; non-endemic residents guess ~0%",
    "kind": "intuition"
  },
  "native": {
    "display": "~1.2–3.4% transmission rate per Ixodes scapularis bite (attachment <72 hrs, endemic area)",
    "numerator": 34,
    "denominator": 1000,
    "unit": "per bite",
    "population": "persons bitten by Ixodes scapularis (deer tick) in an endemic area of the northeastern/upper-midwestern US"
  },
  "normalized": {
    "lifetime_us_adult": 0.25,
    "display": "~1 in 4 lifetime (US adult in endemic region, moderate outdoor exposure)",
    "log_value": -0.6,
    "assumptions": "CDC estimates ~476,000 new US Lyme infections per year (2024 revised estimate, up from the earlier 30,000 confirmed-case figure). US population ~335 million, but roughly 95% of cases concentrate in 15 northeastern and upper-midwestern states with a combined population of ~115 million. Annual per-capita hazard in the endemic footprint ≈ 476,000 × 0.95 / 115,000,000 ≈ 3.93 × 10⁻³. Compounded over 59 adult years: 1 - (1 - 0.00393)^59 ≈ 0.207. Adjusting upward slightly for outdoor-active adults (gardeners, hikers, dog walkers) who accumulate more tick encounters than sedentary residents gives a central estimate of ~0.25, or about 1 in 4 lifetime for a moderately active adult in an endemic state. The uncertainty band spans the sedentary endemic resident (~0.15) to the avid outdoors person in peak-incidence counties (~0.40).\n",
    "uncertainty": {
      "low": 0.15,
      "high": 0.4
    },
    "scope": "subgroup_lifetime"
  },
  "sources": [
    {
      "url": "https://www.cdc.gov/lyme/data-research/facts-stats/index.html",
      "title": "Lyme Disease: Data and Statistics",
      "publisher": "US Centers for Disease Control and Prevention (CDC)",
      "source_type": "govt_report",
      "statistic": "CDC estimates approximately 476,000 people are diagnosed and treated for Lyme disease each year in the United States.",
      "excerpt": "\"CDC estimates that approximately 476,000 people may get Lyme disease each year in the United States. This estimate was derived using methods including insurance claims data, clinical laboratory data, and self-reported physician-diagnosed cases.\"\n",
      "source_date": "2024-03-11",
      "source_accessed": "2026-04-18",
      "archive_url": "http://web.archive.org/web/20260412203222/https://www.cdc.gov/lyme/data-research/facts-stats/index.html",
      "calculation_notes": "The 476,000/year estimate is the population-level anchor. Divided across the endemic-region population of ~115 million (the 15 states that account for ~95% of confirmed cases), the annual per-capita hazard is ~3.93 × 10⁻³. Compounded over 59 adult years: 1 - (1 - 0.00393)^59 ≈ 0.207. With a modest upward adjustment for moderate outdoor activity, the central lifetime estimate is ~0.25.\n"
    },
    {
      "url": "https://www.nejm.org/doi/full/10.1056/NEJM200107123450201",
      "title": "Prophylaxis with Single-Dose Doxycycline for the Prevention of Lyme Disease after an Ixodes scapularis Tick Bite",
      "publisher": "New England Journal of Medicine",
      "source_type": "peer_reviewed",
      "statistic": "3.2% of placebo recipients developed erythema migrans after an Ixodes scapularis bite in a Lyme-endemic area; 0.4% of doxycycline recipients developed it.",
      "excerpt": "\"Erythema migrans developed at the site of the tick bite in 8 of 235 subjects who received placebo (3.2 percent) and in 1 of 247 subjects who received doxycycline (0.4 percent, P=0.04).\"\n",
      "source_date": "2001-07-12",
      "source_accessed": "2026-04-18",
      "archive_url": "http://web.archive.org/web/20251122182322/https://www.nejm.org/doi/full/10.1056/NEJM200107123450201",
      "calculation_notes": "Nadelman et al. 2001 provides the per-bite baseline: 3.2% of placebo recipients (no prophylaxis) developed erythema migrans in an endemic area. This is the per-bite transmission rate used as the native figure. The doxycycline arm (0.4%) informs the prophylactic-doxycycline personal factor multiplier (~0.13×). Subjects had to present within 72 hours of tick removal, so this rate reflects bites with attachment duration up to ~72 hours, biased toward shorter attachments since people who find ticks quickly are over-represented.\n",
      "independence_note": "RCT conducted in Westchester County, NY — independent clinical trial data, not derived from CDC surveillance.\n"
    },
    {
      "url": "https://www.nejm.org/doi/full/10.1056/NEJMcp1316172",
      "title": "Lyme Disease",
      "publisher": "New England Journal of Medicine",
      "source_type": "peer_reviewed",
      "statistic": "The overall probability of developing Lyme disease after a recognized tick bite in an endemic area is approximately 1–3%; with prolonged attachment (>72 hours), the risk rises to roughly 20–25%.",
      "excerpt": "\"The overall risk of Lyme disease after a recognized deer tick bite in endemic regions is only 1 to 3 percent. The risk is essentially zero if the tick is attached for less than 36 hours, rises to approximately 12 percent with attachment of 72 hours, and may be as high as 25 percent if the tick is fully engorged.\"\n",
      "source_date": "2014-10-16",
      "source_accessed": "2026-04-18",
      "calculation_notes": "Shapiro 2014 NEJM review provides the attachment-duration curve: ~0% at <36 hrs, ~12% at 72 hrs, up to ~25% when the tick is fully engorged (roughly 96+ hrs). This underpins the regional_breakdown rows stratified by attachment duration and the personal_factor_multiplier for prompt tick removal vs prolonged attachment.\n",
      "independence_note": "Narrative review synthesizing multiple clinical studies — independent secondary analysis, not derived from CDC surveillance data.\n"
    }
  ],
  "comparison_anchors": [
    {
      "label": "Bee/wasp sting fatality (lifetime, US adult)",
      "lifetime_us_adult": 0.0001267
    },
    {
      "label": "Death in a car crash (lifetime, US)",
      "lifetime_us_adult": 0.0108
    },
    {
      "label": "Shark attack fatality (lifetime, US adult)",
      "lifetime_us_adult": 1.76e-7
    },
    {
      "label": "Melanoma from UV exposure (lifetime, US adult)",
      "lifetime_us_adult": 0.028
    }
  ],
  "regional_breakdown": [
    {
      "region": "Endemic northeast/upper-midwest US (per bite, attachment <72 hrs)",
      "probability": 0.032,
      "notes": "Nadelman et al. 2001 placebo arm: 3.2% per bite. Most recognized bites involve shorter attachment."
    },
    {
      "region": "Endemic US (per bite, attachment >72 hrs / fully engorged)",
      "probability": 0.2,
      "notes": "Shapiro 2014: risk rises to 12–25% with prolonged attachment; 20% is a reasonable midpoint for >72 hrs."
    },
    {
      "region": "Endemic US adult (lifetime, moderate outdoor activity)",
      "probability": 0.25,
      "notes": "CDC 476K cases/yr across ~115M endemic-region population, compounded over 59 years with outdoor-activity adjustment."
    },
    {
      "region": "Non-endemic US (lifetime)",
      "probability": 0.005,
      "notes": "Remaining ~5% of US Lyme cases spread across ~220M people in non-endemic states; lifetime risk rounds to ~1 in 200."
    }
  ],
  "personal_factor_multipliers": [
    {
      "factor": "Outdoor worker in endemic region (forestry, landscaping, farming)",
      "multiplier": 3,
      "notes": "Occupational tick exposure is several-fold higher than recreational; CDC occupational health data."
    },
    {
      "factor": "Avid hiker / hunter in endemic region",
      "multiplier": 2,
      "notes": "Regular woodland exposure during May–September peak nymphal season increases encounter rate."
    },
    {
      "factor": "Prompt tick removal (<24 hrs) after every outdoor session",
      "multiplier": 0.3,
      "notes": "Transmission is near-zero with attachment <36 hrs (Shapiro 2014); diligent tick checks dramatically reduce risk."
    },
    {
      "factor": "Prophylactic doxycycline after recognized bite",
      "multiplier": 0.13,
      "notes": "Nadelman et al. 2001: doxycycline reduced EM incidence from 3.2% to 0.4% (87% relative reduction)."
    },
    {
      "factor": "Resident of non-endemic US state",
      "multiplier": 0.02,
      "notes": "~5% of US cases across ~66% of the population; per-capita risk roughly 50× lower than endemic states."
    }
  ],
  "short_label": "Lyme disease",
  "myth_framing": "calibrated",
  "outcome_severity": "moderate_harm",
  "exposure_pattern": "acute",
  "outcome_type": "recoverable_injury",
  "valence": "negative",
  "caveats": "The normalized lifetime figure applies specifically to moderately active adults living in the 15-state endemic corridor (Connecticut to Minnesota). Outside that footprint, lifetime Lyme risk drops by roughly two orders of magnitude. The per-bite transmission rate depends critically on attachment duration: near-zero under 36 hours, rising steeply after 72 hours. Nymphal ticks (May–July) cause the majority of human infections because they are small enough to go unnoticed; adult ticks, being larger, are found and removed sooner. The 476,000/year CDC estimate includes clinically diagnosed cases that may not have confirmatory serology, so it is substantially higher than the ~30,000 confirmed cases reported through passive surveillance. Post-bite prophylactic doxycycline (single 200 mg dose within 72 hours) reduces transmission by ~87% per Nadelman et al. and is recommended by IDSA guidelines in endemic areas — but this entry does not constitute medical advice.\n",
  "quality_score": {
    "d1": 5,
    "d2": 5,
    "d3": 5,
    "d4": 4,
    "d5": 5,
    "d6": 5,
    "d7": 4,
    "d8": 5,
    "avg": 4.75,
    "scored_by": "claude-code-8d",
    "scored_at": "2026-05-25",
    "methodology_version": "1.2"
  },
  "reviewer": "likelier-phase-11-agent",
  "last_reviewed": "2026-04-18",
  "reviewed": true,
  "generated_at": "2026-04-18",
  "image": {
    "alt": "A single stylized deer tick on a pale leaf, flat vector illustration in muted earth tones."
  },
  "attribution": "Likelier — https://likelier.app",
  "license": "https://creativecommons.org/licenses/by-sa/4.0/",
  "support": "https://buymeacoffee.com/kgluszczyk?via=likelier&utm_content=api-fear-single",
  "canonical_url": "https://likelier.app/lyme-disease-tick-bite"
}