Example inspection data
| Site | Date | Houses inspected | Houses positive | Containers inspected | Containers positive | HI% | CI% | BI |
|---|---|---|---|---|---|---|---|---|
| Backyard | 2026-01-20 | 20 | 2 | 55 | 3 | 10.00 | 5.45 | 15.00 |
| Greenhouse | 2026-01-27 | 12 | 1 | 30 | 2 | 8.33 | 6.67 | 16.67 |
| Community plot | 2026-01-31 | 25 | 0 | 68 | 1 | 0.00 | 1.47 | 4.00 |
Formula used
How to use this calculator
- Inspect your garden and nearby areas after rain or watering.
- Count inspected properties and containers with standing water.
- Mark containers positive if larvae or pupae are seen.
- Enter counts in Single Survey, or use Batch Survey for multiple rows.
- Press Calculate. Results appear above the form.
- Download CSV or PDF to keep a weekly prevention record.
Survey coverage and sample size
Reliable indices start with consistent coverage. Inspect all reachable water-holding spots: buckets, trays, gutters, drums, and plant saucers. Record houses inspected as properties checked, not rooms. Aim for at least 10–30 properties per neighborhood and 30–100 containers per session. Larger samples reduce volatility, especially after rainfall events that create temporary breeding sites. Include shaded patios and roof corners where water collects.
Interpreting HI, CI, and BI together
House Index shows how widespread breeding evidence is, while Container Index reflects how concentrated breeding is within inspected containers. Breteau Index combines both by expressing positive containers per 100 properties. For example, HI 10% and CI 5% can still produce BI 15 if positives are clustered across fewer properties. Use all three to avoid overreacting to a single percentage. Pair results with a quick container map.
Trend tracking across weeks
Single readings are useful, but trends are stronger. Repeat surveys weekly during warm, wet periods and after major irrigation changes. Compare the same route and container list to keep results comparable. Watch for sudden BI jumps after storms; this often points to overlooked ground-level puddles or clogged drains. Document dates, notes, and corrective actions to link changes to results.
Targeted source reduction actions
Prioritize containers that repeatedly test positive. Empty and scrub saucers, cover barrels, and keep lids tight. Flush drains, level low spots, and store tools upside down. Replace standing water in birdbaths every few days and brush biofilm. For ornamental ponds, improve circulation and remove debris. Focus on eliminating larvae habitat first, then reassess indices to confirm impact.
Reporting and recordkeeping
Exports support professional tracking. Store CSV files with consistent naming, such as site-date-route. Use the PDF report for quick sharing with teams or homeowners. In batch mode, compare sites side by side to identify hotspots and allocate labor efficiently. Add notes on weather, irrigation schedules, and disposal methods so your historical records explain why indices moved. Include followup photos.
FAQs
What counts as a positive container?
A container is positive when mosquito larvae or pupae are seen in the water. If uncertain, treat it as positive and recheck after cleaning. Use a flashlight and inspect shaded edges where larvae hide.
Can I use properties instead of houses?
Yes. Enter the number of properties, yards, or plots you inspected as “houses inspected.” The indices still work because they rely on consistent units across surveys.
How often should I run surveys?
Weekly surveys work well in warm or wet seasons. Also run a survey 24–72 hours after heavy rain or a major irrigation change to catch newly filled containers.
Why can Breteau Index be high with a low Container Index?
Breteau Index uses positive containers per 100 properties. If you inspect few properties but many containers, a handful of positives can raise BI even when CI stays low. Review both metrics together.
What if I have zero inspected values?
Indices require a positive denominator. Enter at least one inspected property and one inspected container. If you have no access that day, record notes separately and survey again when feasible.
How do I interpret batch results?
Batch mode summarizes average HI, CI, and BI across rows. Use it to compare sites and dates, then prioritize the highest BI locations for source reduction. Export CSV for spreadsheets and PDF for quick sharing.