Why is only one in nine suspected leptospirosis cases confirmed?

The figure comes from the Ministry of Public Health weekly epidemiological bulletin, which publishes it without comment. It deserves comment.

Where does the figure come from?

From the bulletin for epidemiological week 23 of 2025. In that particular week three suspected cases were notified and no new confirmations. The year to date total through that week was 205 suspected and 23 confirmed.

Leptospirosis carries immediate mandatory notification, which means it is notified on clinical suspicion, without waiting for the laboratory. That is a correct and deliberate decision: it forces the system to find out early. But it also means the suspected count and the confirmed count measure different things, and that the distance between them is information in itself.

Why does it matter particularly in this disease?

Because treatment works better the earlier it starts, and because the initial symptoms resemble dengue, which is far more common in the country. A febrile presentation in the rainy season admits several readings, and the one chosen determines which test is ordered.

Put plainly: clinical suspicion is not a formality preceding confirmation. In practice it is the moment treatment is decided. Confirmation arrives afterwards and serves mainly to know what is happening in the country, which is a different and also necessary function.

What could explain the distance?

Several things, and here it is worth being honest about what the public figure allows us to distinguish: it does not allow us to distinguish them. There are at least four reasonable hypotheses, and they do not exclude one another.

• That many suspected cases were not leptospirosis. A broad case definition captures noise on purpose, so as not to miss real cases.
• That the sample never reached the laboratory, or arrived in poor condition.
• That the test was taken too early. In leptospirosis, serology can read negative in the first days of symptoms and positive a week later.
• That the result exists and never returned to the surveillance system, which is a circuit problem rather than a laboratory one.

The four have different fixes, and three of them are cheap. Which is why it matters to know which one weighs most.

Can that be measured?

Yes, and without building anything new. Three dates suffice, and most are already recorded: when symptoms began, when the sample was taken, and when the result came back.

With those three dates across a year of cases, what is currently mixed comes apart. If few days systematically separate symptom from sample, the problem is test timing. If many separate sample from result, the problem is the circuit. If neither distance is striking, then the likely explanation is the first one, the case definition, and that is a useful answer too.

It is a question answerable with what is already collected. It does not need a system, it needs three fields put in order.

What this analysis does not claim

It does not claim there are undiagnosed leptospirosis cases. The distance between suspected and confirmed is not an estimate of missed cases, and treating it as one would be a mistake.

It does not claim the laboratory performs poorly. Of the four hypotheses, two have nothing to do with the laboratory and one expressly exonerates it.

And it does not compare territories. The bulletin publishes that breakdown; this piece uses only the national total, because a provincial comparison on these numbers would produce more noise than signal.

Sources

Weekly epidemiological bulletin of the Dirección General de Epidemiología, epidemiological week 23 of 2025, the source of the 205 suspected cases, the 23 confirmed and the three notified that week. The immediate mandatory notification on clinical suspicion is stated in the same bulletin, in the SINAVE operational indicators section.