Вчера у сестры была высокая температура и боль в горле, поэтому другой врач заподозрил ангину.

Russian usually expresses possession with the pattern у + genitive + быть.

So у сестры была высокая температура literally means something like at the sister there was a high temperature, but in natural English it means the sister had a high temperature.

This is a very common structure in Russian:

• У меня есть брат = I have a brother
• У него была машина = He had a car

In the present tense, есть is often omitted in everyday speech:

• У сестры высокая температура = The sister has a high temperature

Сестры is the genitive singular of сестра.

That happens because the preposition у requires the genitive when it means at or is used in the possession pattern:

• сестра → nominative
• у сестры → genitive after у

So у сестры means at the sister / the sister has.

This is a very common Russian pattern in existential sentences, especially when the verb comes before a list of things.

Russian often uses singular agreement in this kind of structure:

• была высокая температура и боль в горле

The verb is singular feminine because it matches the first noun, температура, which is feminine singular.

You may also see были высокая температура и боль в горле, with plural agreement. That is also possible. But была is very natural when the sentence is presenting symptoms as a single situation: there was a fever and a sore throat.

Yes. Высокая температура literally means high temperature, and it is a very normal everyday way to talk about a fever in Russian.

So when Russians say someone has температура, they often mean body temperature is elevated, especially in a medical context.

A more formal or different word is лихорадка, but высокая температура is extremely common and natural.

Боль в горле literally means pain in the throat, and this is a standard Russian way to express a sore throat.

Here:

• боль = pain
• в горле = in the throat

Горле is the prepositional singular of горло, because after в meaning location, Russian uses the prepositional case:

• горло → nominative
• в горле → prepositional

A very common alternative expression is:

• У неё болит горло = She has a sore throat / Her throat hurts

It can mean either another doctor or a different doctor, depending on context.

In this sentence, it most likely means that one doctor was mentioned or implied earlier, and then a different doctor looked at the situation and suspected this diagnosis.

So другой врач often carries the idea of contrast:

• not the same doctor as before
• some other doctor

This is about aspect.

Заподозрил is perfective, and it means the doctor came to suspect or formed the suspicion at a particular moment.

That fits this sentence well: the doctor saw the symptoms and then suspected a diagnosis.

By contrast, подозревал is imperfective and would usually suggest an ongoing state:

• Он подозревал ангину = He suspected it was tonsillitis / He was suspecting tonsillitis

So заподозрил highlights the moment when the suspicion arose.

Ангину is the accusative singular of ангина, because заподозрить takes a direct object:

• заподозрить что? → ангину

So:

• ангина = nominative
• ангину = accusative

Also, this is an important vocabulary point: Russian ангина does not usually mean the same thing as English angina in the heart-related sense.

In Russian, ангина usually means tonsillitis, often something like strep throat in everyday translation.

So learners should be careful: this is a false friend.

Поэтому means therefore, so, or that is why.

It connects the first clause and the result:

• she had these symptoms,
• therefore another doctor suspected tonsillitis.

The comma is there because Russian is joining two clauses:

• Вчера у сестры была высокая температура и боль в горле
• поэтому другой врач заподозрил ангину

This punctuation is completely normal in Russian.

Russian word order is flexible, and putting Вчера first sets the time frame right away.

It gives the sentence a natural topic-comment structure:

• Yesterday, as for what happened then, the sister had a high temperature and a sore throat...

You could move вчера to another position, but sentence-initial placement is very common and natural when giving background information such as time.