Legionellosis

Legionellosis recorded 2,065 cases in this reporting window. In the latest observation 2026-08-30, it reported 38 cases, +3 cases versus 35 in previous observation 2026-08-23 (+8.6%). The latest four observations changed +26% versus the prior four, so this is not just a one-period twitch. The combined judgement is Declining, with low risk (21).

• Current movement: Declining; latest 38 cases, +3 cases versus the previous observation (+8.6%)
• Recent momentum: latest four observations versus prior four +26%; long-window change -4.4%
• Seasonal context: No same-season baseline; same-season median ratio no same-season baseline, based on — same-season baselines
• Historical position: latest value is at the no historical percentile of prior observations
• Scope limit: This source is sentinel surveillance; counts reflect reported sentinel signals and should not be read as total national infections. The current source does not provide death-count fields, so missing values should not be interpreted as absence of mortality burden.

• The short-term rise has case-volume support: the latest observation is +3 cases above the previous observation, not merely a low-denominator percentage artifact.
• Seasonal context is No same-season baseline: YoY -30%, same-season median ratio no same-season baseline. The historical percentile is not extreme, so this reads more like a rapid rise within a seasonal upswing that needs confirmation over subsequent observations.
• Risk is low, but not the highest priority tier; keep it in active review rather than classifying it as an event-level outbreak from this signal alone.
• This source is sentinel surveillance; counts reflect reported sentinel signals and should not be read as total national infections.

Trend judgement: Declining. The important point is not simply that the latest count is high; three pieces of evidence line up. First, the latest observation is +3 cases above the previous one. Second, the latest four observations changed +26% versus the prior four, indicating a steeper recent slope. Third, the long-window change remains -4.4%, so the background is also moving upward. With a same-season ratio of no same-season baseline and historical position at the no historical percentile, this should be treated as a seasonal/elevated rise that needs confirmation. Review prefecture distribution, age groups, sentinel coverage or reporting completeness, and any school or childcare-cluster signals next.