A disease with no national count, and the reason is where people go for care

Haemophilia is an X-linked genetic disorder, primarily affecting males,
causing a deficiency in a blood-clotting protein — **factor VIII in haemophilia
A, factor IX in haemophilia B**. About one in 5,000 males is born with it,
and A is roughly four times as common as B.

It causes **spontaneous internal bleeding and excessive bleeding after injury
or surgery**, and can lead to **repeated bleeding into the joints and the
chronic joint disease that follows, neurological damage, damage to other organ
systems, and death.**

The gap

**No precise national US prevalence estimates for hemophilia exist because
of the difficulty identifying cases among persons who receive care from
various types of health care providers.**

The reason is worth separating from the obvious one. This is not because
haemophilia is rare — one in 5,000 male births is a large number of people. It
is because there is no single place they all appear. Someone might be seen
by a haematologist, a paediatrician, an emergency department or a specialist
centre, and no system joins those up.

Two state-based studies estimated prevalence at **13.4 and 19.4 per 100,000
males** — a range of nearly 50% between two studies of the same country,
which is what an uncounted disease looks like.

What makes surveillance possible anyway

Those same studies found the thing the surveillance system is built on:

As of January 2020 the United States had 144 such centres.

So while no system sees everyone, a network of 144 centres sees most
patients and nearly all of the severely affected ones. Surveillance through
those centres is not a complete census, and it is close to complete for the
people at highest risk — which is the group whose outcomes the system most
needs to track.

That is the compromise this report evaluates: **Universal Data Collection
(1998–2011)** and Community Counts (2011–2019), two successive surveillance
programmes built on the treatment centres because the alternative — a national
count — does not exist.

*Source: Centers for Disease Control and Prevention, MMWR Surveillance
Summaries.*